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A method for glare analysis
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A method for glare analysis
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INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zed) Road, Ann Atbor MI 48106-1346 USA 313/761-4700 800/521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A METHOD FOR GLARE ANALYSIS by Shweta Arun Japee A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF BUILDING SCIENCE December 1995 Copyright 1995 Shweta Arun Japee Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1379586 Copyright 1995 by Japee, Shweta Arun All rights reserved. UMI Microform 1379586 Copyright 1996, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, M I 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U NIV ERSITY O F SO U T H E R N CALIFORNIA THE SCHOOL OP ARCHITECTURE UNIVERSITY PARK LOS ANGELES. CALIFORNIA 90069-0291 This thesis, w ritten b y .SjX&gJk ...A & V . N .. TAf &5r..... under the direction o f hcS. .. Thesis Com mittee, and a p proved b y all its members, has been pre sented to and accepted b y the Dean o f The School o f Architecture, in partial fulfillm ent of the require m ents fo r the degree o f Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS I am convinced that I must be singularly lucky to have so many people looking out for me, while providing me with the help and encouragement to complete this thesis. Professor Marc E. Schiler, at the School of Architecture, University of Southern California, who has provided me with all the help, encouragement, support and feedback not only towards completing this work but in everything I have undertaken. I don’t think I can thank him enough; my deep gratitude goes to him. My parents, who have always been extremely supportive of whatever we chose to do; my love to them and my family. My gratitude goes to the School of Architecture; without the funding provided through a scholarship, I would not have been able to come to USC at all. To Professor G. Goetz Schierle and Professor Douglas Noble who as committee members have provided me with positive feedback and advice towards the direction of my thesis. Many thanks to all my friends, who have always urged me to keep moving forward. A special thanks to everyone in the Building Science Program and Prof. Schiler, Diane and family, for making this program feel like a big family. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS TITLE PAGE.............................................................................................................. I ACKNOWLEDGEMENTS....................................................................................... ii LIST OF FIGURES.................................................................................................... v ABSTRACT...............................................................................................................vi INTRODUCTION.......................................................................................................1 CHAPTER 1 THE LUMINOUS ENVIRONMENT...................................................5 1.1 Light and vision............................................................................. 5 1.2 Factors in visual performance........................................................ 8 1.3 Task conditions...............................................................................9 1.4 Lighting conditions.......................................................................12 1.5 The observer................................................................................. 15 CHAPTER 2 PHOTOMETRIC QUANTITIES........................................................17 2.1 Solid angle..................................................................................... 18 2.2 Luminous energy .........................................................................19 2.3 Luminous flux................................................................................ 19 2.4 Luminous intensity........................................................................ 20 2.5 Illuminance....................................................................................21 2.6 Luminance.....................................................................................22 CHAPTER 3 DISCOMFORT GLARE..................................................................... 23 3.1 Types of glare................................................................................23 3.2 Glare evaluators............................................................................ 27 3.3 Analysis of glare phenomena........................................................ 36 CHAPTER 4 METHODS OF MEASURING LUMINANCE..................................38 4.1 Luminance meters......................................................................... 38 4.2 Video photometry........................................................................ 40 4.3 Conventional photometry Vs video photometry.......................... 41 4.4 Luminance distribution method....................................................42 4.5 Significance of making luminance measurements........................ 44 iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 5 EVALUATION OF LUMINANCE DISTRIBUTION METHOD... 45 5.1 Description of the method.............................................................45 5.2 Description of equipment..............................................................46 5.3 Measuring the results....................................................................47 5.4 Gathering data...............................................................................47 5.5 Analysis......................................................................................... 48 5.6 Observations.................................................................................. 54 5.7 Conclusions................................................................................... 65 CHAPTER 6 TESTING THE METHOD..................................................................67 6.1 Design of the experiment..............................................................67 6.2 Description of equipment..............................................................68 6.3 Testing and recording ..................................................................69 6.4 Occupant survey............................................................................70 6.5 Capturing the video images...........................................................71 6.6 Gathering data...............................................................................72 6.7 Analysis..........................................................................................72 6.8 Observations.................................................................................. 75 6.9 Conclusions................................................................................... 85 CHAPTER 7 RECOMMENDATIONS AND FURTHER WORK......................... 88 7.1 Conclusions................................................................................... 88 7.2 Recommendations..........................................................................89 APPENDIX A ..........................................................................................................91 APPENDIX B .........................................................................................................116 APPENDIX C ........................................................................................................124 REFERENCES........................................................................................................171 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES 1.1 A cross section of the human eye..................................................................... 6 1.2 Visual response for (a) scotopic and (b) photopic vision.................................7 1.3 Field of view...................................................................................................... 8 1.4 Visual angle........................................................................................................9 2.1 The visible spectrum........................................................................................17 2.2 Solid angle........................................................................................................ 19 2.3 Relationship between luminous flux, intensity and illuminance.....................20 2.4 Illuminance and luminance..............................................................................21 3.1 Direct glare...................................................................................................... 24 3.2 Veiling reflections............................................................................................26 3.3 Reflected glare.................................................................................................27 4.1 The Minolta luminance meter......................................................................... 39 4.2 Luminance box................................................................................................43 5.1 Numerical analysis of histograms.................................................................... 52 5.2 Color code........................................................................................................53 5.3 March 27, 3:00 p.m., Room 1........................................................................ 55 5.4 March 27, 5:00 p.m., Room 1........................................................................ 57 5.5 April 5, 5:00 p.m., Room 1.............................................................................59 5.6 April 5, 5:00 p.m., Room 2 .............................................................................60 5.7 October 2, 12:00 p.m., Room 1...................................................................... 62 5.8 October 2, 12:00 p.m., Room 2...................................................................... 64 6.1 Example of rating scale...................................................................................70 6.2 Numerical analysis of histograms....................................................................73 6.3 Occupant response...........................................................................................74 6.4 March 28, 8:11 a.m......................................................................................... 76 6.5 March 28, 8:24 a.m......................................................................................... 78 6.6 March 28, 8:49 a.m......................................................................................... 79 6.7 March 28, 8:54 a.m..........................................................................................81 6.8 April 1, 8:38 a.m..............................................................................................83 6.9 April 1, 8:39 a.m..............................................................................................84 6.10 Occupant response to contrast ratio between high intensity and background...............................................................................................85 v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Occupant interaction with lighting and lighting control systems has been found to significantly effect the energy use patterns of spaces. The extent of occupant interaction with lighting controls depends on the degree of visual comfort or discomfort experienced by the occupant in the space. Visual discomfort in a space is primarily caused due to high contrasts, and luminance variations in the field of view of the occupant. Glare and occupant response and attitude to it causes significant changes in the predicted energy requirements of the space but its effect has not yet been included in determining energy use patterns. This study aims to develop a method for glare analysis using the Luminance Distribution Method, based on recorded luminance variations in a space. Glare and occupant response to it is studied in terms of contrast changes and luminance variations within the space. The method is based on actual contrast ratios and occupant behavior within the space. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION Light has always been recognized as one of the most powerful factors available to mankind, capable of putting man in touch with his environment. The relationship between people, light and form is intimate. Man has always tried to articulate this relationship with light through his buildings. Initially all buildings were designed around the single fixed source of light: the sun. The shapes and sizes of rooms, details and color within them were determined by the amount of daylight entering and what the appearance would be like when sunlight poured in. But ever since artificial light was found to be easier to control and design with, we have ignored the quality of the luminous environment while providing adequate levels of illumination. Although it signifies major advances in techniques, good lighting calls for much more than the mere provision of adequate illumination. It includes concerns about achieving visual comfort in a space, lighting quality and occupant satisfaction, rather than just trying to provide certain prescribed light levels in our designs. A good luminous environment is one in which what we want to or need to see is emphasized, and what we do not need to see is hidden or played down without any accompanying feeling of discomfort or distraction. Recent trends in lighting design have been to increase the level of illumination by increasing the brightness of the fixtures or providing larger windows, with an aim to providing a good lighting environment. While there is a marked improvement in the task performance by increasing light levels, the discomfort which results from such large bright sources in the field of view detracts from 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the benefits of higher illumination. Designing for visual comfort within a space includes not only providing sufficient light for task performance but also the elimination of discomfort caused due to glare, veiling reflections etc. Visual discomfort in a space is primarily caused due to high contrasts and luminance variations in the field of view of the occupant. It is clear that occupant sensing and photo sensing lighting controls in buildings, succeed in reducing their electrical as well as air conditioning requirements, but the effect of glare or visual discomfort on the occupant and the resulting interaction with the lighting control systems has not yet been included in determining energy use patterns. It is also not clear how glare and visual discomfort effects occupant attitude and productivity in a space and how the subsequent modifications made by the occupant governs the performance of the lighting systems within the space. Glare, and occupant response and attitude to it cause significant changes in the predicted energy requirements of a space and hence needs to be carefully evaluated. At first, glare or discomfort was understood to be caused due to high levels of illumination in a space 1 . But the simple understanding that the higher light levels outside a building did not cause discomfort, radically changed this thinking. Glare was then thought to be caused because of the high contrast ratios within the room. By experimentation, it was found that a ratio of 10:1 was problematic, and would cause discomfort within the space, and that achieving maximum contrast ratios of 3:1 within a space would make the space comfortable 2 . However this theory can be disproved easily. 1 Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office, 1963 2 Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office, 1963 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A clean sheet of paper with dark black ink printing on it has a contrast ratio of more than 10:1, and does not necessarily cause glare. There have been many theses proposed about glare behavior. The first glare theory was developed by Hopkinson in his Glare Index Method3 4 5 . Based on extensive experimentation and subjective testing he proposed that glare was dependent on the background light level within a space. This method seemed to address the complex phenomenon of glare in terms of contrast between the high intensity glare source and background luminances. Visual Comfort Probability6 7 8 is the current state of the art method to determine comfort within an interior space. Comfort is estimated on the basis of how many people out of 100 would feel comfortable within the space. Relative Visual Performance91 0 is another existing method in which the comfort within a space is defined on the basis of the speed and accuracy of performing a task. This method, although suitable for determining performance at a single task, is not capable of evaluating the luminous quality of the entire space. The underlining concern therefore in glare evaluation 3 Hopkinson, R. G., Evaluation of Glare, Illuminating Engineering, Vol. LII, June 1957, Pg. 305 4 Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office, 1963 5 Hopkinson, R. G., Pctherbridge, P., Longmore, J., Daylighting, Hcinemann, London 1966 sDiLaura, David L., On the Computation of Visual Comfort Probability, Journal of the Illuminating Engineering Society, Vol. 5, July 1976, Pg. 207 7 Subcom. on Direct Glare(1972), Preamble by Calculation Procedures Com.(1991), Computing Visual Comfort Ratings for Interior Lighting, RQQ Report No. 2 with the 1991 Preamble Outline of a Standard Procedure for Computing Visual Comfort Ratings for Interior Lighting, IES LM42, 1991 8 Guth, S. K., Computing Visual Comfort Ratings for a Specific Interior Lighting Installation, Illuminating Engineering, Vol. LX!. Pg. 634. 9 Rea, Mark S., Toward a Model of Visual Performance: Foundations and Data, Journal of the Illuminating Engineering Society, Vol. 15. Summer 1986, Pg. 41 I0Rea, Mark S., Toward a Model of Visual Performance: A Review of Methodologies, Journal of the Illuminating Engineering Society, Winter 1987. 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is the need to be able to numerically compare all the luminances within a field of view simultaneously to the background light level of the space. It is very difficult to measure and quantify luminances in the field of view. Typical luminance measurements do not describe the visual phenomenon. Rather Luminance meters111 2 either average the visual field at some angle of view to provide a single number value or measure the detail within the visual field of some specifically interesting point. Video Photometry131 4 has been found to offer the ability to map and characterize the visual environment. However there are extensive calibrations required to offset camera gains, settings, responsivity etc. The Luminance Distribution Method1 5 offers a solution to the prevalent drawbacks of video photometry like recording f-stop, range, etc., by introducing a known luminance box into the image which acts as a self calibration scale. This thesis aims to develop a method for glare analysis using the Luminance Distribution Method, based on recorded luminance variations in a space. Glare and occupant response to it is studied in terms of contrast changes and luminance variations within the space. The method is based on actual contrast ratios and occupant behavior within the space. 1 1 Subcommittee on Guide for Measurement of Photometric Brightness of the Illuminating Engineering Society, IES Guide for Measurement of Photometric Brightness (Luminance), Illuminating Engineering, Vol. LVI, July 1961, Pg. 457 1 2 Walsh, J. W., Photometry, Constable, Lewin and Baker, London, 1958, 3rd Edition. 13OrfieId, Steven J., Photometry and Luminance Distribution: Conventional Photometry versus CapCalc, Lighting Design and Application, Januaiy 1990 1 4 Rea, Mark S., Jeffrey, I. G., A New Luminance and Image Analysis System for Lighting and Vision, Journal of the Illuminating Engineering Society, Vol. 19, Winter 1990, Pg. 64 1 5 Schiler, Marc E., Report of Luminance Study Method, July 1994 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.0 THE LUMINOUS ENVIRONMENT Vision is the primary sense by which we absorb information about a building. Since any discussion of light and visual comfort is primarily related to vision, it has to be discussed in context of the basic facts of human vision. While it may be possible to provide sufficient levels of light at a comfortable level to perform a task, there is, however, no guarantee of it being comfortable. The distinction between amount of light and acuity, brightness, color, and contrasts needs to be understood in order to evaluate the luminous environment. This chapter gives an overview of the human eye and how it functions, before proceeding to discuss the various aspects of the luminous environment. 1.1 Light and Vision The human visual system provides contact with the external world, and is used to translate light color and shapes to the brain. The eye is responsible for the initiation of the total visual process. It consists of three layers, - the sclera, a hard structure modified at the front of the eye into a transparent layer called the cornea. The second layer is called the choroid, a black membrane which absorbs light and prevents inter-reflections. This layer is modified at the front into a transparent lens which focuses light accurately on the third layer, the retina (Fig. 1.1). The retina is responsible for the sensitivity, it is here that the light receptors are located. The retina contains a large number of tiny light receptors called rods and cones. The cones are chiefly distributed along the back and center of the retina with a small 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. indentation called the fovea - the focal point of the lens during normal daylight conditions. Cones provide color reception. Different cones are sensitive to different wavelengths of light producing color vision. Rods are distributed more widely along the edge of the eye, and are extremely light sensitive and function well at low light levels. They have no color sensitivity. They are less densely packed and hence there is less precise resolution of details. Each cone is linked to the visual center of the brain by a one-to one neural link, whereas rods are grouped to single nerve paths, which is another reason for the difference in resolution between rod and cone vision. Fig. 1.1 A cross section of the Human eye Source: Schiler (1992) The visual sensation varies from day to night, altering the acuity, or sharpness, of vision. Day vision is called photop' c vision, and night vision is called scotopic vision. For scotopic vision, the peak visual response shifts from the daytime level of 555 nm to the RETINA opnc NERVE 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. night time level of 505 nm (Fig. 1.2). It takes the eye 1 hour to fully adapt to this shift in wavelengths. Extremely low levels of surrounding illuminance (.Ifc ) or 1 lux is required for full rod vision to take place. One lux is equivalent to the ambient light at night from stars and reflected starlight. Photopic vision is highest at 555 nm, which has a color of yellow similar to that of the sun. & 1 ■ BSJ W avelength, nm Fig. 1.2 Visual response for (a) scotopic and (b) photopic vision. Source: Robbins (1986) There are limits to the brightness that can be tolerated by any particular field of view. Vision within a 60 degree solid angle, that is 30 degrees in any direction around the centerline of the foveal vision, is called the near surround. Within this region, the eye can detect differences in brightness between the object and its foreground or background. At 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the extreme edge is the far surround, or peripheral vision whose size varies because of the overlap in the fields of view of both eyes (Fig. 1.3). This adaptation process, luminance and adaptation ranges of the human eye are important for determining visual comfort conditions. 6C T 30* 30* Fig. 1.3 Field of view Source: Robbins (1986) 1.2 Factors in Visual Performance The basic visual tasks are the perception of contrast, fine detail and brightness gradient. Assuming a good lighting environment, that is a low glare, acceptable brightness ratios and a pair of unfatigued eyes, visual performance depends on the size of the task and the luminance, contrast and adaptation levels within the space. The Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. components of any visual task are the object or task conditions, the lighting conditions within the space and the observer himself. 1.3 Task Conditions 1.3.1 Size of the Visual Task The size of the visual task is the measure of the angle subtended by the eye at the detail (Fig. 1.4). It is defined as the ratio of the size of the detail to the distance from the eye.1 6 The visual angle is determined by a = 57h/D where h = height of object in feet and D = distance of object from eye in feet. Fig. 1.4 Visual Angle Source: Egan (1983) 1 6 Hopkinson. R. G., Kay, J. D„ The Lighting of Buildings, (1969) 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3.2 Brightness The sensation of vision is caused by light entering the eye. Brightness is the perception of the amount of light received at the eye. It is the mental appraisal, at a given adaptation level of the luminance in the field of view. Brightness exists only in the experience of the observer and not only does it vary with luminance, size and surroundings but also with the viewers state of adaptation (adjustment of the visual system to a sort of average field brightness). Any effort to translate brightness to ’uminance without taking into account the adaptation will give high errors. When adapted to a fully dark space, all brightness is above the adaptation level, at adaptation level of 1 cd/m2 , brightnesses are divided below and above the adaptation level and at high adaptation levels, all brightnesses are below that level. The eye can detect brightnesses over a range of one trillion (101 2 ) to one. At any one instant the eye can detect a range of 1 to 1000. The lower levels are accomplished after an adjustment period called the adaptation time varying from 2 minutes for cone vision to forty minutes to an hour for rod or scotopic vision. Areas and surfaces may increase in luminance by raising the illumination level, but the ratios of adjacent surfaces will not change. A white paper on a dark desk will have high contrast at all levels of illumination. Desks with similar reflectances can be separated or distinguished in brightness by using different levels of illumination. Reflectance is a more active factor in brightness than is illuminance. We perceive reflectance as brightness so we feel that it remains a constant, although the illumination is constantly changing from 10 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dawn to dusk, from clear to cloudy days. Color plays an integral part since it defines the spectral quality of light. Hence in general, visual performance increases with object brightness, however it depends a great deal on the background against which it is viewed, and the subsequent contrast in brightness between the object and its surroundings. 1.3.3 Contrast Contrast (C) can be expressed as (C) = (Lb- L0 ) Lb where Lb= Luminance of task (fL) and L0= Luminance of surround (fL). It is the sensation of difference between juxtaposed things and since contrast is a sensation, it is resident in the observer and cannot be measured directly. To perceive a difference between two visual sensations, they must be compared. Contrast is a vital element of efficient visual perception. Contrast is desired between the object to be viewed and its immediate surround. The size of the letters, sharpness of detail and the time taken to read it are also critical. Sensation also changes with the adaptation of the viewer. Luminance contrasts remain the same at all adaptation levels, however the visual appraisal of contrast changes. At lower adaptation levels, the higher values appear light, while others appear black. As adaptation rises, one can distinguish more of the lower contrast values. 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. At high adaptation levels, low contrast values are clear while high contrast values tend to glare. The human eye is more sensitive to contrast at high levels of adaptation than at low levels. 1.4 Lighting Conditions 1.4.1 Quantity of Light Visual Acuity is a function of the quantity of light. The greater the illumination, the smaller the detail that can be seen. In the same way, the amount of light falling on the visual task determines the difference in brightness between the task and the background. The higher the illuminance the greater the differences in brightness or contrast that is visible. The sense of color is also affected by the light levels. Seeing is aided by higher lighting levels in three ways: by perceiving finer detail, smaller difference in brightness or contrast, as well as color. Any task can be analyzed in terms of critical detail, contrast and color difference, and sufficient illumination must be provided for this recognition in any given environment. 1.4.2 Quality of Light Good lighting demands not just sufficient levels of illumination but also a uniform light distribution within the space. Glare and contrast affect the visual comfort within a space. Visual comfort or discomfort relates to the field of vision, since there are definite limits to brightness that can be tolerated for different angles of field of view. The eye works most comfortably when the object on which it is concentrated is 12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. preferentially bright. Other bright sources of light act as distractions, and if they are excessively bright in relation to the surroundings, they cause discomfort or pain. Excessively colorful areas, flickering light etc. can draw attention and cause irritation. Good lighting design involves avoiding all forms of distraction and discomfort. Under daylighting, glare results from the very bright sky as seen through a large window. Under artificial lighting conditions, glare arises through a direct view of excessively bright light sources. Glare is a function of contrast, if a bright light is seen in dark surroundings, it will cause more glare than if seen in light surroundings. There are two aspects of glare which need to be watched out for in interior lighting design, glare which arises because of harsh contrasts between juxtaposed areas and glare which arises because of areas of excessive brightness such that the visual mechanism gets saturated. Avoiding any sort of discomfort due to glare is the key issue. Discomfort due to glare causes not just a complaint, it can also affect the general efficiency of the worker as a result of annoyance, frustration etc. as well as force the occupant to interact with his immediate surroundings to get rid of the temporary feeling of discomfort, for example letting down the blinds, or turning on the lights. 1.4.3 The task and its surroundings - Luminance patterns The lighting of the whole environment is also equally important, not only because it adds character to the environment but also because it influences the visibility of the task itself. General lighting of the entire space is at present the visual practice in 1 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. natural as well as artificial lighting. Nevertheless many people feel an instinctive preference for some selective light on their own work place. In the need to consider the lighting of the surroundings, we have to take into account certain characteristics of the eye itself. The eye is drawn naturally to things which are bright or to things which are markedly different from the general run of objects which comprise the visual scene. Bright colors and bright lights attract attention. So if a particular visual task is to be concentrated upon, the task can be highlighted by making it brighter or more colorful than the rest of the surroundings. Experimental work has determined that best vision results when the work is lighted brighter than its surroundings, and the greatest comfort results when there is a gradation of brightness from the visual task itself as the brightest area in the visual field, through an intermediate zone to a moderate level of brightness in the general surrounding. Comfort also depends on the distribution of brightness. It is usually preferable for the work to be a little brighter than the surroundings. Maximum comfort appears to arise if the general surroundings in the room as seen by the worker at his task are between one third and one tenth of the brightness of the task itself and that there is an advantage if the brightness of the work is graded through and intermediate surround (e.g. desktop) into the general surroundings such that the ratio of brightness (luminance) of the work : intermediate surroundings : general surroundings is of the order of 10:3:1 1 7 1 7 Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office. 1963 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.4.4 Color Color affects the human nervous systems in different ways. The perception of color is associated with the emotions of the individual as well as the actual stimuli produced. Color is appreciated as a combination of the spectral reflection characteristics of a surface and the spectral composition of the light illuminating the surface.1 8 The color of the illumination (light) as well as the corresponding coloration of objects within a space constitutes an important facet of the quality of light within a space. 1.5 The Observer 1.5.1 Sight and Recognition What we see depends not only on the image which is focused on the retina but also on the intelligence which interprets that image. The interpretation which we make of the visual environment will depend not only upon our visual capacity for registering the image but also on the intelligence to make that interpretation. 1.5.2 Age and Visual Performance Visual performance decreases with age. The eyes require a longer time for adaptation and focussing, because the lens becomes stiffer and less flexible, and are 1 8 Robbins, C. L., Daylighting Design and Analysis, Pg. 25 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. increasingly sensitive to glare. Hence as the age increases, normal sighted people need higher levels of illumination reaching their task for optimum performance. 1.5.3 Adaptation The human being adapts in a number of ways to his environment, physiologically, in a sense that there are physical changes in the body (metabolic rate change etc. ) and psychologically. Adaptation is the ability to adjust the sensitivity of the system to the average condition of the environment. Adaptation alters the sensitivity to amount, quantity, and to change or contrast. For example, on a bright day, if we look indoors, it is dark but as we come indoors and give our eyes the time to readapt to the darker room, things look bright. Adaptation plays a marked role in architectural lighting, it changes our appraisal of the magnitude of things, for example, glare from headlights. On a dark unlighted road, a pair of oncoming headlights looks extremely bright, and will cause glare and discomfort. On a well lit street, they do not look so bright. However in daylight the same headlights cause no glare at all and look no brighter than the surroundings. Adaptation alters the sensation by changing both the apparent brightness and also the degree of discomfort. The human eye can react to a range of luminances from less that 1 millionth of a fL to 10,000fL (equivalent to luminance of snow). But it cannot see this entire range at one adaptation level. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.0 PHOTOMETRIC QUANTITIES In discussing glare, and its relationship with lighting and vision, a basic understanding of the definition of light, its behavior, and qualitative and quantitative measurements is necessary. Light as defined by IESNA1 9 is the visually evaluated radiant energy, or simply as a form of energy that permits us to see. The human environment is exposed to a wade variety of natural and man-made energy sources that emit energy within various bands of the electromagnetic spectrum. Visible light is a narrow band of radiation in the electromagnetic spectrum, having a wavelength from about 3.8 x 10"7 m to 7.6 x 10'7 m (Fig. 2.1). io " 10 10 Microwave Ultraviolet Cosmic rays Infrared../ Radio Television Power Visible spectrum :: Infrared Green Red 200 nm 300 400 500 600 700 800 900 1000 nm Fig. 2.1 The Visible Spectrum Source: Schiler, (1992) 1 9 D B S, EES Lighting Design Handbook, 5th Edition, 1972, Pg. 2.1 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Expressed in nanometers, the range of visible light is from 380 nm to 760 nm. The human eye perceives the 555 nm light the best, i.e. the color of light similar to sunlight. Daylight produces energy over the entire spectrum, in equal quantities, which appears as white light. Light obeys certain physical laws and characteristics. Before discussing the qualitative aspects of light, it is necessary to understand some physical terms and terminology involved. These lighting quantities are defined according to human vision, and whether the light is a point source or an extended source, the physical characteristics remain the same. The following definitions of lighting terms are adapted from “ Simplified Design o f Building Lighting” , Chapter 2.5-2.8 by Marc Schiler and “ Mechanical and Electrical Equipment fo r Buildings", Chapter 18.5-18.8 by Benjamin Stein, John S. Reynolds, and William J. McGuiness. 2.1 Solid Angle A solid angle (co) is the ratio of the area on the surface of a sphere to the square of the radius of a sphere. It is expressed in steradians. A sphere with radius 1 foot has an area of 47t square feet. Each one square foot on this sphere subtends a solid angle of one square foot area per one foot radius, and thus one steradian. A sphere has a total of 4 7 1 or 12.57 steradians. This is a way to express the relationship between the light source, treated as a point and the light energy that it emits (Fig. 2.2). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 2.2 Solid Angle Source: Schiler, (1992) 2.2 Luminous Energy Luminous energy (Q) is the amount of energy transmitted in the visual spectrum. It is measured in lumen-seconds or Talbots (T). 2.3 Luminous Flux Luminous flux ( < ) > ) is the amount of light, output from a light source, small or extended, irrespective of the direction of light. It is the time flow rate of light energy. If we take a light source and surround it with an imaginary sphere at a fixed distance the luminous flux through a defined area on that sphere is the amount luminous energy flowing through the defined area (Fig. 2.3), 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It is expressed as < j ) = dQ/dt The unit in both the English system and Systeme International (SI) is lumen-second per second or lumen (lm). 2.4 Luminous Intensity The amount of light emitted by a source in a specific direction is called the luminous intensity (I). It represents the force of the source that generates light. It is defined as the luminous flux on the surface of an imaginary sphere per unit solid angle. I = d c f> /d c o S p h e ric a l s u rfa c e ___ I K ra d iu s S p h e ric a l s u rfa c e 1 ft* in a r e a • T otal flux o f 1 lu m e n T o ta l flux 1 2 .5 7 lu m e n s Light s o u r c e 1 c a n d e la Illu m in a n ce 1 f c o r 1 Im /tt2 o r 1 0 .7 6 lux Illu m in a n ce 1 lux o r 1 Im /n t? o r 0 .0 9 2 9 fc Fig. 2.3 Relationship between Luminous flux, Intensity and Illuminance Source: Stein, Reynolds, McGuiness, (1986) 20 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Luminance intensity is measured in two units. The candlepower (cp) measures the amount of energy emitted in all directions by a single candle. Candela (cd) measures the rate at which the energy is leaving the source in a specific direction. The magnitude of a candela is the same as a candlepower, but the definition is more exact. A luminous intensity of one candlepower is one lumen passing through one steradian of the sphere. The luminous intensity of one candela is the luminous flux of one lumen passing through one steradian in the direction normal to that steradian (Fig. 2.3). 2.5 Dluminance The light energy arriving at a surface is called the illuminance (E). It is the luminous flux density intercepted by a surface at a given distance from the light source or luminous flux per area of the surface. E = dcp/dA -Illuminance: 100 fc or 100 lm/sq.ft. Light Sourcer'"'" 100 candelas or 1257 lumens output I n m im n iy ' (100 lux or 100 lm/sq.m) * Transmittance of surface Fig. 2.4 Illuminance and Luminance Source: Stein, Reynolds, McGuiness, (1986) 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The unit of measurement is the foot-candle (fc) in the English system and lux (lx) in the SI system. One lumen of luminous flux, uniformly incident on one square foot of area, produces an illuminance of one foot-candle (Fig. 2.4). One lumen of luminous flux on one square meter of area produces one lux. The relation between lux and foot-candle is given by 10.764 lux = 1 foot-candle 2.6 Luminance The light energy leaving a surface is the luminance. The total luminous flux density leaving a surface in a given direction, per unit area of the surface as viewed fr^m that direction is the luminance (L) (Fig. 2.4). L = [d2 /dodA] cosG, where 0 is the angle between direction of observation and the normal to the surface. Units are footLamberts (fL) in the English units or candela per square meter in the SI units. One footLambert is equal to 1 /t c candela per square foot. Luminance can also be described physically as the brightness of a surface. A general definition is that it is the portion of the illuminance of the surface reflected or transmitted. L = E x p or L = E x t where p = reflectivity and t = transmittance of the surface. Luminance is used to describe the objective physical attribute of brightness and luminosity is used to describe the subjective response to brightness. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.0 DISCOMFORT GLARE Visual comfort is taken to mean the absence of a sensation of physiological pain, irritation or distraction. Visual comfort within a space depends on the contrast levels and luminance variations across the space. Glare is the chief cause of visual discomfort. It is the result of unwanted light in the visual field, and is usually caused by the presence of one or more sources of excessively bright light. Although brightness and brightness contrast are important in visual communication, excessive contrast between foreground and background can disrupt the human eye’s ability to distinguish objects from the background and perceive detail. The human eye can function well over a wide range of luminous environments, including starlight (.03 cd/m2 and clear sky 10,000 cd/m2. However it cannot function very well if such extreme levels of brightness are present in the field of view at the same time. The extent to which a particular source of light interferes with a person’s ability to perform a task and the resulting discomfort the light causes are two different aspects of glare. 3.1 Types of Glare 3.1.1 Disabaity Glare Disability glare is that aspect of glare which results in a direct reduction in the persons ability to see objects within the visual field. The presence of bright light sources can directly affect the ability to see (Fig. 3.1). Brilliant light sources, like the car headlamps at night, or the view of the sun from a window at the end of the corridor 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. are examples. This disability is not easy to recognize, but is visible in the increase in the number of errors at task or decrease in speed of task performance. Fig. 3.1 Direct Glare The disabling effect of the light source is a direct function of the luminous intensity of the glaring source in the direction of the eye, whether this intensity is from a large source of lower brightness or a small source of high brightness. It is also a function of the contrast between light and dark in the field of view. A large window with a low brightness sky may cause disability to vision, especially in the areas immediately around it. The disabling effects of the glare source are due to a veil of brightness being cast over the field of view. Hence, if the rest of the space is at a high light level, the disability will pass completely unnoticed than if the room were dimly lit. The eye is not be able to adapt simultaneously to the bright source as well as dim 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. background and this causes the disability. The severity of the disability is reduced by raising the general level of brightness in the field of view. 3.1.2 Discomfort Glare Glare in which there is no significant reduction in the ability to see, although discomfort still persists due to bright sources in the field of view is called discomfort glare, e.g. the view of an excessively bright sky near the line of sight of a worker. Discomfort glare is influenced by the brightness of the glare source rather than by the intensity i.e., it is the brightness of the source rather than the amount of light which it is emitting, and in particular its relationship to that of the surroundings. The sensation of discomfort glare is a function of the brightness of the light source and the apparent size of the aperture. The degree of discomfort caused by a glare source will be reduced by an increase in the brightness of the surroundings. Discomfort glare sensation seems to be caused due to two sensations. One is due to the contrast produced when a bright light source is seen in a visual field of lower brightness. The other sensation is caused due to the saturation effect produced when the retina is stimulated for maximum response. The eye can maintain this response only for a short length of time before fatigue occurs. Discomfort glare includes the sensations of distraction, annoyance and dazzle. While the disabling effects of glare can be measured by objective methods like noting a change in visual acuity, discomfort effects of glare rely on experiments 25 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. involving a series of subjective tests which attempt to correlate subjective responses to discomfort, to the changes in contrast ratios and luminances variations in the space. 3.1.3 Veiling Reflections Veiling reflections occur when an image of a source of light is brighter than the luminance of the task, e.g. image of a window or a luminaire reflected off the surface of a VDT screen, whereby rendering the screen impossible to see (Fig. 3.2). Fig. 3.2 Veiling Reflections This is a form of disability glare. Essentially the discomfort results when small areas of the task reflect light reducing contrast between the task and immediate surround. For example, pencil handwriting is highly susceptible to veiling reflections, as pencil graphite acts as small mirrors. 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.1.4 Reflected Glare Reflected glare occurs when the light from a bright source is reflected off a surface directly into the eye or into the field of view causing discomfort e.g. specular surfaces (Fig. 3.3). If the reflections are of high luminance and of significant area, they may produce disability glare near the line of sight. Bright reflections of small size produce enhancing reflections called sparkles, which are usually intentional. Fig. 3.3 Reflected Glare 3.2 Glare Evaluators Glare is a subjective response, different for each individual, and hence cannot be given any absolute value. However, in order to determine on a scientific basis the necessary standards of lighting in a building, it is necessary to break down the characteristics of visual comfort, visual acuity and task performance, and express this 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. relationship in terms of brightness, contrast ratios and adaptation levels. These have been the basis of glare evaluation methods to date. 3.2.1 Visual Comfort Probability (VCP) Visual Comfort Probability is a rating that expresses the discomfort glare produced by an interior lighting system in terms of the percentage of occupants who do not find the system uncomfortable. VCP2 0 ’ 21,22 is a function of 1. The luminaires’ average luminance. 2. Solid angle subtended by luminaire at observer position. 3. The position of the luminaire with respect to the observers line of sight. 4. Average luminance of field of view. 5. Number of luminaires in field. Computation of VCP is based on the indices of sensation of the luminaires in an observer’s field of view, (M;). These indices are functions of the position of the luminaires with respect to the observer and room’s surface luminances. These indices in turn define the DGR (Discomfort Glare Rating) of the lighting system. For any one ■^DiLaura, David, L„ On the Computation of Visual Comfort Probability, Journal of the Illuminating Engineering Society, IES Transaction, Vol. 5, July 1976, Pg. 207 2 1 Guth, S. K., Computing Visual Comfort Ratings for a Specific Lighting Installation, Illuminating Engineering, Vol. LXI, Pg. 634 2 2 Subcom. on Direct Glare (1972), Preamble by Calculation Procedures Com. (1991), Computing Visual Comfort Ratings for Interior Lighting, RQQ Report No. 2 with the 1991 Preamble Outline of a Standard Procedure for Computing Visual Comfort Ratings for Interior Lighting, IES LM42, 1991 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. observer position and viewing direction, the average field luminance F produced by all luminaries interacting with the room surfaces is a constant. It is expressed as a set of discrete values M(0,v|/) defined as functions of 2 perpendicular Plane Angular Coordinates (0,y). From this data, an interpolating series is developed, which is used to calculate M; of all the luminaires in the field of view. F = (Lc(< o c-©,) + (U )t + Lf + L w C o w ) x 1 5 where Lc = average ceiling luminance in fL. Lw = average wall luminance in fL. Lf = average floor luminance in fL. < d c = Solid angle subtended by ceiling for that position. c o w = solid angle subtended by a wall for that position. co f = solid angle subtended by the floor for that position. oj, = 2 O; = sum of solid angles subtended by each luminaire. (Lb), = 2 LjO; — sum of average luminances of luminaires weighted by the subtended solid angles of each. 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The computational power of this procedure is in its ability to express the total effect of a given rectangular array of luminaires as a simple function of observer location. VCP however does not rate the overall acceptance of the visual environment in spaces. This computational procedure is of considerable detail. In essence it uses the point method to determine the discomfort index for each luminous element in the field of view and combines them to obtain the overall rating of the lighting system. It is heavily dependent on the coefficients and standard conditions adopted and tables provided by the IES for these standard lighting conditions. VCP tables were developed based on standard room size, luminaire size and location, wall and ceiling luminances as well as typical task locations. To apply these tables to specific lighting installations will require the determination of certain values in the calculation procedure, rather than directly using the constants provided by the IES. 3.2.2 GLARE INDEX The Glare Index Method is a method proposed by R. G. Hopkinson 2 3 ,2 4 ,2 5 which correlates lighting quality and subjective evaluation to the physical characteristics of the room and its lighting. It is a subjective empiricism of the degree of visual discomfort in a room. 2 3 Hopkinson, R. G., Evaluation of Glare, Illuminating Engineering, Vol. LH, June 1957, Pg. 305 2 4 Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office, 1963 2 5 Hopkinson, R. G., Petherbridge, P., Longmore, J., Daylighting, Heinemann, London, 1966 30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The basic glare formula assesses glare discomfort on the basis of the luminance and size of the source as well as the general level of light within the space and is proposed as G’ = f(Bs)f(Q) fdyfC B O fC O ) where 1. Luminance of the light source (BJ 2. Size of the light source (Q) 3. General level of adaptation (Bb) 4. Position of the sources and field of view (0) 5. Luminance of the surrounds to the source (Bi) Glare or discomfort is caused by two distinct situations, first the eye may be dark adapted and the presence of a bright source acts as an emotional affront. These sources may not be so bright that the eye cannot adapt to their luminance, it is simply their presence in the darker field that causes the discomfort. The second situation arises when the whole field or large part of it is extremely bright and the eyes are fully light-adapted but still unable to adjust themselves to the high luminance. Luminances of the order of snow in full sunshine are of this category. 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The practice to establish the glare constant G is to use the basic glare formula defined as G = B,1 '6 Q°'8 B,,10 for each source within the space. Hence, the Glare constants G’, G” etc. for each source at the same background luminance Bb is calculated individually, G’ = B,-16 Q°-8 and G” = B...1 '6 Q0 8 Bb10 where Bs. and Bs- is the luminance of the different sources. Hence the Glare constant G for the entire installation is given by G = £ (G’ + G” + G’” + ...... ) The glare constant obtained is examined on a mean probability diagram derived from a 50 member study conducted by the Building Research Station 2 6 . It is based on the findings from the experiments that 1. The mean for the experienced six man team on whose judgments the glare constants are based on correspond to the 85 % probability level on the 50 member study. 2 6 Hopkinson. R. G., Lighting, 1963 32 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2. The mean judgment of glare for the general population in any given situation is one criterion less glaring than that of the six man team. From this Index, an estimate of the percentage of the general population who will receive any sensation of glare in any given situation whose glare constant has been evaluated is determined. The Glare Index, though a complex method, is still a measure of the physical characteristics of the room and the lighting within it. All the factors which make up the glare index are physical quantities which are measurable, i.e. the brightness and size of glaring sources. However once we evaluate it on an index as developed by the B.R.S., based on results from experiments we derive one numeral with subjective connotations. Then by setting limiting values of Glare Index, as done by the IES, we are laying down conditions which may give rise to discomfort. The glare index is a complex evaluation which is based on the hypothesis that physical characteristics evaluated in a subjective way, give us a good guide to the lighting quality in terms of discomfort due to glare. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.3 RELATIVE VISUAL PERFORMANCE MODEL Relative Visual Performance 27,2 8 (RVP) is defined to be the speed and accuracy of performing a visual task. RVP is a calculation procedure to establish visual performance. The RVP method is based on two premises: 1. Visual performance is distinct from task performance. Task performance is a combination of both visual and non-visual factors, contributing to behavioral response. 2. The visual performance model should be consistent with basic visual response. Sensory responses are characterized by compression. Small changes in stimulation about the adaptation level produce corresponding changes in sensation. Compression is widely accepted as a basic general description of sensation including visual sensation or visual response to luminous modulations as is the premise for this model. A single photoreceptor (rod or cone) comprises of many photosensitive units, which produce an electric potential between the photoreceptor and its environment. When a photon is captured by one of the photosensitive units in the photoreceptor, there is a voltage drop produced along the photoreceptor. Photon catches by other receptors produce similar voltage drops, however subsequent depolarization has relatively less influence on the total response. 2 7 Rea, M. S., Toward a Model of Visual Performance: A Review of Methodologies, Journal of the Illuminating Engineering Society. Winter 1987, Pg. 128 2 3 Rea, M. S., Towards a Model of Visual Performance: Foundations and Data, Journal of the Illuminating Engineering Society, Vol. 15, Summer 1986, Pg. 41 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Performance is defined in terms of time and errors at a reading-writing task is strongly affected by the different luminous contrasts between the white paper and the ink. Contrast measurements of the ink calibration squares is calculated by - L, Lb where Lt is the luminance of the calibration square, and Lb is the luminance of the paper adjacent to the calibration square. Visual performance is studied as contrast changes between paper and ink, or task contrasts, and the effect of any glare source in the field of view of the occupant or a change in the adaptation level in a space is accounted for in the change in time taken to perform the task and the number of errors produced. It could be used by lighting practitioners as an interim algorithm for calculating relative visual performance at numeric reading tasks, however it in no way describes the quality of the visual environment. The confounding problem of visual and nonvisual contributions limits the utility of the calculation procedure, as one does not know how much of the behavior is based on visual responses under the control of the lighting designer, and how much is non visual, for example psychological, intellectual, motor, emotional etc. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.3 Analysis of Glare Phenomena Based on the above discussed methods and crucial factors in determining the physical factors which govern discomfort from glare, it is emphasized that the results are not substitutes for experience in lighting practice but rather to assist in the quantitative interpretation of the complex problem of discomfort glare. Bright light sources cause glaring effects, which impair visual efficiency. This may be brought about by a direct disabling effect or it may result from irritation and discomfort. It has been found that discomfort glare is primarily a function of the balance between the brightness and intensity of the glare source on one hand, and the brightness of the surroundings on the other; the higher the brightness of the surroundings, the less discomfort will be caused by the glare source. Since the eye is limited in adaptation, the discomfort caused by large sources of high brightness may not be capable of reduction by increasing the brightness of the surroundings. Also it has been shown that small reductions in the brightness of large glare sources, such as windows, results in a useful decrease in discomfort. Visual comfort can be assessed by several methods, some of which are direct, and some indirect. Indirect Methods for example, have been the measurement of the rate at which the observer blinked or the rate at which his heart was beating during the experiment. These experiments showed that some correlation exists between the probability of the difficulty of the visual task, and the physiological factors under measurement. Other indirect measurements have been associated with the performance 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the visual tasks, where it is assumed that the speed of performance and number of mistakes is influenced by the degree of discomfort experienced in the space. However here again, no direct correlation between performance and degree of discomfort has been established. These indirect methods have been used because of the unreliability of the Direct Methods. There is nothing easier than confronting a subject and asking him to describe the discomfort, but unfortunately most subjects when asked this question are unable to give consistent and reliable answers, and tend to be vague and inaccurate, which is useless as a quantitative measure. The Multiple Criterion Technique 2 9 is a method which trains the subjects to make reliable assessments. It is a method of direct appraisal in which the subject is confronted with conditions which can be varied over a wide range. One condition at a time can be varied while the rest being kept constant. These conditions are varied over a wide range so that all sensations of discomfort from imperceptible to intolerable are experienced. This method has been proven to be accurate and reliable, and is useful as a method to quantify relationships between the physical variables which govern discomfort. Hence it has been used as the basis of the new glare analysis method and in the research conducted towards developing the method. ’ Hopkinson, R. G., Evaluation of Glare, Illuminating Engineering, June 1957, Pg. 305 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.0 METHODS OF MEASURING LUMINANCE Visual comfort is about luminances, contrasts and brightness of surfaces in the field of view. What we perceive is not the illuminance on a surface, but the light that is leaving that surface or the luminance of the surface. To be able to accurately evaluate the visual environment, it is necessary to understand this distinction. A good lighting environment is not just one which has adequate levels of light (illumination) to complete the task, but also which has no excessive contrasts, and bright areas in the field of view. So in fact, when we evaluate the visual environment, in terms of comfort, excessive brightness, too much glare, etc. we are talking of the luminances in the field of view. Hence to be able to quantify glare and contrasts in the field of view and the overall visual comfort within the space, it is necessary to be able to measure the luminances within the space. 4.1 Luminance Meters Luminance photometers 3 0 ’ 3 1 consists of a photovoltaic detector with a photopic correction filter, connected to an amplifier with a display. It has suitable optics to image an object onto the detector. Typically they detect light over a large angle. A means of viewing the object is usually provided so that the area that is being measured as well as the surrounding field is made visible. Changing the focal length of the 3 0 Subcommittee on Guide for Measurement of Photometric Brightness of the Committee on Testing Procedures of the Illuminating Engineering Society. IES Guide for Measurement of Photometric Brightness (Luminance), Illuminating Engineering, Vol. LVI, July 1961, Pg. 457 3 1 Walsh, J. W., Photometry, Constable, Lewin and Baker, London, 1958,3rd Edition 38 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. objective lens will change the field of view and thus the size of the measurement field. Various aperture sizes can be used to define the measured area (Fig. 4.1). \Tp' W Fig. 4.1 The Minolta Luminance meter Source: Courtesy Minolta Luminance meters are equipped with a hooded cell arranged to block oblique light and calibrated in units of luminance (footLamberts or Lamberts). This permits direct observation of the measured area during measurement. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2 Video Photometry Video photometry,3 2 a recent trend, offers the ability to map and characterize the visual environment. This process uses video cameras incorporating CCD’s (charge- coupled devices). The system consists of a camera, an image acquisition board (IAB) and a microcomputer. On instruction from the software, the IAB freezes and digitizes the luminance pattern viewed by the camera. The analog signal is converted to digitized signal by the converter, and consists of many thousands of individual bit values corresponding to each pixel of the camera’s CCD array. By suitable calibration the bit values are processed by the microcomputer to provide the luminance values at the corresponding points in the field of view. Typical video cameras scan 250-500 horizontal scans with analog information in the horizontal scan is roughly equal to 500 points. This is equivalent to 125,000 individual luminance meters placed over the area. Video photometry is fast and convenient especially where it is necessary to obtain a large number of luminance values. ‘CapCalc’,3 3 called the Capture/Calculate system was developed by Dr. Mark Rea at the National Research Council of Canada, uses video photometry as a tool to measure luminances. It provides photometry by the following five step procedure 3 2 Orfield, Steven J., Photometry and Luminance Distribution: Conventional Photometry versus CAPCALC, Lighting Design and Application, Jan. 1990, Pg. 8 3 3 Rea, Mark S., Jeffrey, I. G„ A New Luminance and Image Analysis System for Lighting and Vision, Journal of the Illuminating Engineering Society, Vol. 19, Winter 1990, Pg. 64 40 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1. Capture a video image on the camera. 2. Scan the image for digitization 3. Calibrate the image based on the zoom and aperture settings. 4. Develop the photometric values of the 250,000 or so luminance points on the digitized image. 5. Call up and analyze the video image. 4.3 Conventional Photometry Vs Video Photometry A photometer measures instantly whereas video photometry takes a few seconds to capture, digitize and calibrate the image. Thus if an evaluation in terms of a single number is needed, it might be advisable to use a photometer, but if more complex and statistical information is required the photometer is less capable. The photometer is of high precision whereas the video is of high definition and can more easily be used to measure over time. The important decision here to be made is what is to be analyzed. If the measurements are needed for later analysis, video photometry becomes more useful than conventional photometry. If necessary, the camera can measure and analyze a far smaller area than any hand held luminance meter, or it can zoom out and handle an entire room. It is this flexibility which makes it more useful. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.4 Luminance Distribution Method The Luminance Distribution Method 3 4 is one step further in video photometry. It offers a solution to the prevalent drawbacks in video photometry like recording f-stop, range, extensive calibration to offset camera gains, settings and spectral responsivity. Video cameras are nonlinear in their response. Each sample point results in an analog reading which is digitized, on a scale of 0-255 in intensity, basically the range which can be handled by the camera. The brightest point (say 1000 fL) would turn up as 255 in intensity and the 0 fL area would turn up as 0 in intensity, however due to the nonlinear pickup of the camera it was not necessary that the 500 fL would turn up as 125 in intensity. Cameras cannot handle a full range of intensities without an irising mechanism like that of an eye. The f-stop determines the amount of light being let into the camera and which is sampled or recorded. Video cameras automatically adjust the aperture to provide the optimum amount of light for the pickup surface. This means that the 0-255 range could be either 0-1000 fL or 0-5000 fL, depending on the f-stop during the recording. The Luminance Distribution Method is based on the idea that rather than recording the f-stop and the non-linearity of the pickup for each recording, a known luminance box can be introduced into the image acting as a self calibration scale. This 3 4 Schiler. Marc E., Report of Luminance Study Method, July 1994 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ensures that the known luminance will always be in the pickup range of the camera, either at the high intensity end, the low intensity end or somewhere in between. Since the image is now certain in absolute value, other portions of the image could be determined in relation to or calibrated from this known absolute value. The known luminance box uses long life fluorescent lamps and opal glass diffusers to provide a known luminance of 250 fL (Fig. 4.2). Each box has an absorptive surface of approximately 0 fL providing 2 surfaces within the image, one at 0 fL and the other at 250 fL, to provide the range of pickup. Fig. 4.2 Luminance Box The images can be analyzed in terms of overall luminance, luminance distribution, contour maps or histograms, individual luminance, contrasts, luminance ratios, etc. Apart from these it is also possible to record the view outside the window, position of the blinds, solar position and resulting shadows and sunspots and the 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resulting occupant behavior in the space. The luminance readings from the digitized images can be correlated with the simultaneous recording of illuminance and occupant behavior within the space. The ability to make recordings over time, and to be able to record user interaction with controls and lighting systems within the space, are the advantages of this system, along with its capacity to provide absolute values of luminances rather than just a range of intensities. 4.5 Significance of making Luminance Measurements While evaluating glare and visual comfort, it may be necessary to know, not only the individual luminances of small areas of an interior, but also the average luminance of a larger area and measure a sort of average luminance of the view. Typical luminance measurements do not describe the visual phenomenon. Rather luminance meters either average the visual field at some angle of view to provide a single number value or measure the detail within the visual field to describe some specifically interesting value e.g. a maximum or minimum luminance value. With these measurements calculations for Glare Index etc. could be performed. These results are however in no way proportional to the complex visual environment. To evaluate the complex behavior of adaptation levels, field of view, and source luminances, it is necessary to make use of video photometry, whereby the luminance of an entire view (general background level) and individual surface luminances can be measured simultaneously. 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.0 EVALUATION OF LUMINANCE DISTRIBUTION METHOD In this chapter the study conducted at the Collins Center is described. The study focuses on using the new Luminance Distribution Method 3 5 to measure luminance variations within a space. The aim of this research is to determine a method of glare analysis in terms of contrasts and luminance variations across a space and based on an understanding of the existing glare theories. 5.1 Description of the Method The important factors which were taken into consideration while conducting the study were 1. Measurement of available illuminance. 2. Behavior of occupants within the situation. 3. Record the luminous environment in order to have information available over time and over a number of surfaces within the field of view of the occupants. This study is concerned with the third aspect, of recording and measuring luminances and the corresponding occupant behavior within the space. 3 5 Schiler, Marc E., Report of Luminance Study Method. July 1994 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2 Description of Equipment 5.2.1 JVC Camera Two JVC GR-M7 3 6 Camera-Recorders with time exposure capabilities which can be operated remotely were used for recording within the space. The camera is equipped with a nickel-cadmium battery which is connected to the AC outlet through an AC Power Adapter/Battery Charger AA-V10U. 5.2.2 Luminance Box Two identical Luminance boxes 3 7 capable of providing a constant known luminance over a period of time were built. A fluorescent ballast and tube are placed inside a reflective box with a high density opal glass diffuser. This surface is backlit to a high luminance and is less susceptible to changes within the room. The other cavity is lined with flat black paper and covered with a semi transparent gauze. This cavity has a luminance of below 1.0 fL across a broad range of illuminances. The fluorescent fixture uses an F8T5WW lamp manufactured by Lampi of Japan. The boxes are calibrated for lamp lumen depreciation and dirt depreciation. The original luminance distribution across the surfaces were measured under various illuminance conditions using a Minolta meter at distance of 2m from the surface. These measurements were again taken after a year at the conclusion of the experiment. The corrections were made at the end of the experiment.3 8 3 6 JVC GR-M7 Camera-Recorder/Playcr Instruction Manual. 3 7 Schiler, Marc, Report of Luminance Study Method, 1994. 3 8 Schiler, Marc, Report of Luminance Study Method, 1994. 46 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.3 Measuring the Results The boxes were located so that there was a minimum effect on them from other light sources in the room. They were located against a window wall and below the desk level. This made sure that there was no exterior sunlight and direct artificial light hitting the known luminance box. The JVC cameras were mounted below an air-conditioning duct facing the wall and the perpendicular wall closest to the window and the task location at the computer monitor. The luminance of the view outside, position of blinds, solar position, position of sunspots and shadows within the room and comparison of the luminance of the wall with that of the monitor was recorded. Data was gathered for different combinations of lightshelf, skylight and control situations. The illuminance readings were recorded using a Campbell datalogger with Licor illuminance sensors within the room. 5.4 Gathering Data The digitized images show specific cases of high contrast as well as luminance changes across the space. The images vary from room to room depending on whether the lightshelf is installed or not and what time of day and year was recorded. Occupant behavior is recorded in terms of whether the Venetian blinds were let down or not and whether the occupant changed his task location to escape the feeling of discomfort. The histograms project the relative range of intensities across the space, number of pixels at 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. those intensities as well as the percentage of field of view the background and high intensities occupy. 5.5 Analysis The collected data was analyzed in terms of 1. Histograms of the intensity distributions within the space 2. Recorded images of the space. The observations were first based on the histograms. After the histogram was analyzed for potential glare, contrast ratios and percentage of field of view, the images were then analyzed to see if the analysis from the histograms seemed appropriate. 5.5.1 Analysis of histograms The histograms of the scanned video images are analyzed in terms of its distribution and absolute ranges of intensities. The relation between the bell curve and the spike presents a way to find out the relationships between the background adaptation level and various intensities within the space. 1. Shape and distribution of bell curve: There is often a distinct bell curve observed in the histograms of images of almost all the days tested. This bell curve can be assumed to be representative of a background level. The shape of the bell curve is also sensitive to the luminance distributions within the space. A wider bell curve implies a more uniform distribution of light intensities over the space. A narrow higher bell curve implies that 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. most of the background is at a smaller range of intensities, with few points at an extreme range. A curve crowded towards the left indicates that most of the background is at a lower level with a few bright areas or pixels present at the higher levels. A curve shifted towards the right indicates that most of the field is at a higher level, with a few dark spots present within the space indicated at the lower levels. 2. Field of View: For most field of views, there is a linear relationship between the number of pixels in an image and the actual steradians of the field of view. Hence by evaluating the number of pixels at the background intensity or at the high intensity level, and comparing them to the total number of pixels in the image, the percentage of the field of view which either the background or the glare source occupies can be established. Since there can be a relation established between number of pixels and steradians in the field of view, the histogram can provide critical information about the percentage of field of view occupied by the background or the glare source. Another important factor is what percentage of the field of view is required in order to produce glare. From the numerical analysis, it can be established that in almost all the cases a percentage of 70-80 defines the background. The high intensity area occupies around 5-10% of the field of view. It should however be noted that any change in the percentage of field of view of the potential glare source causes an equivalent change in the shape and distribution of the bell curve or background levels. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3. Relative Range of Intensities: The histograms also provide a relative range of light intensities which are present in the space. These are then correlated with the color coded images of the space to get the absolute values of the intensities. However, just their relative range of intensities provides useful information. There are ratios of 1:200 to 1:250 between the highest intensity and lowest intensity levels within the image. Not all of them produce discomfort. It is the ratio of intensities between the background level and the highest intensity which is more critical to glare analysis, and can be established from the histograms. This is especially true if the background is at lower intensities. 4. The spike: The spike indicates the intensity reached by the maximum luminance values of pixels in the space. The position of the spike on the histogram and its relation to the bell curve determines the visual comfort within the room. A spike at the low intensity indicates that most of the background is at a low intensity. The problem arises when there is a spike at the high intensity end on the histogram. This spike could be a potential high intensity glare source such as a window, table top, wall surface, or the known luminance box itself. This can be determined by examining the images. The relation between the spike at the high end and the bell curve establishes the contrast between the background levels and potential high intensity glare source, which is consistent with the conclusion that it is the background level which defines glare or no glare situations. The percentage of field of view which the high intensity occupies is also determined from the histograms. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.5.2 Numerical Analysis: 1. Median Pixel Intensity: This is the relative intensity of the median pixel in the bell curve distribution (Fig. 5.1). 2. Weighted average Intensity: This is the average of the product of each intensity level and the number of pixels at that intensity. This gives equal importance to each pixel and its intensity. 3. Number of Background Pixels: The total number of pixels which constitute the background or correspond to the bell curve portion of the histogram. 4. Total number of Pixels: This is the total number of pixels in the image, amounting to approximately 150,000. 5. Percentage of view: This is the percentage of the entire field of view which the background pixels occupy. 6. Maximum Intensity: This corresponds to the intensity of the median pixel of the possible glare source. 7. Ratio: This is the contrast between the intensity of the median pixel of the glare source and the background level. 8. Percentage of View: This is the percentage of the field of view the possible glare source or any surface at the highest intensity occupies. 51 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. N u m erical A n a ly sis o f H is to g ra m s NAME MEDIAN PIXEL INT Imp WEIGHTED AV. INT. Iw NO.OF B.PIXELS TOTAL PIXELS V. VIEW MAX INT Im RATIO Im/lmp RATIO Im/lw NO.OF MAX.INT PIXELS % VIEW GLARE ANALYSIS 03273PM1 67I 67.73 134218 151040 88.90% 235 3.51 3.47 10260 6.80% NO GLARE [63273PM2 64 56.98 129508 151040 '8570% 226 3.53 3.97 7326 4.90% [INTERNAL GLARE 03275PM1 63 60.01 131292 151040 86.90% 238 3.78 3.97 4397 2.90% INO GLARE 03275PM2 65 58.4 123316 151040 81.60% 247 3.8 4.23 666 0.40% NO GLARE 04053PM1 54 56.66 130454 151040 86.4% 236 4.37( 4.16 10040 6.6% GLARE 04053PM2 NO DATA GLARE 04055PM1 52 50.21 124046 151040 82.1% 235 4.52 4.68 5140 3.4% INTERNAL GLARE 04055PM2 67 60.46 141944 151040 94.0% 242 3.61 4 2164 1.4% GLARE CORRECTED iQQ23PM'i 49 48.73 125049 151040 82.8% 234 '4.78 4.8 10090 6.7% NO INTERNAL GLARE 10023PM2 73 74.32 122133 151040 80.9% 233 3.19 3.14 14309 9.5% NO GLARE 10029AM1 46 50.53 128153 151040 84.8% 223 4.85 4.41 9702 6.4% NO GLARE 10029AM2 78 79.95 123152 151040 81.5% 232 2.97 2.9 12911 8.5% NO GLARE T65212PM 1 49 49.96 128000 151040 84.7% 231 4.71 4.62 11563 7.7% NO INTERNAL GLARE 100212PM2 80 iB O .61 125276 151040 82.9% 230 2.88 2.85 13886 9.2% NO GLARE 10026PM1 72 64.8 134461 151040 89.0% 236 3.28 3.64 3721 2.5% NO GLARE (i(X)26PM2 92 84.23 128441 151040 85.0% 245 2.66 2.91 1566 1.0% NO GLARE 12211PM1 69 70.52 131484 151040 87.10% 233 3.35 3.3 11742 7.8% NO INTERNAL GLARE 12211PM2 97 92.34 132709 151040 87.90% 238 2.45 2.58 2237 1.50% GLARE CORRECTED 12212PM1 65 69.39 i 29755 151040 85.90% 234 3.6 3.37 11451 7.60% NO GLARE 12212PM2 96 93.21 134508 151040 89.10% 245 2.55 2.63 402 0.30% GLARE CORRECTED 12231PM1 73 70.87 132492 151040 87.70% 234 3.21 3.3 12062 7.99% NO INTERNAL GLARE j 2232PM1 68 65.53 120116 151040 79.50% 243 3.57 3.71 1416 0.90% NO INTERNAL GLARE Fig. 5.1 Numerical A nalysis of H istogram s 5.5.3 Analysis of recorded images The absolute values of luminances are available from the images. The images are color coded, each color corresponding to a specific range of intensities (Fig. 5.2). With this code, the luminances of various surfaces, within the room and specifically in the field of view of the occupant can be identified. Color Relative Intensity Ranee Black 0-32 Dark Green 32-64 Dark Blue 64-96 Purple 96-128 Light Green 128-160 Yellow 160-192 Light Blue 192-224 Red 224-256 Fig. 5.2 Color code The color of the known luminance box gives us the relative scale needed to establish the absolute values of other surfaces in the field of view. For example if the 250 fL known luminance is at the relative 100 level, then the highest pixels corresponding to the right end on the histogram are at approximately 637 fL. The image is then analyzed to find out which surface corresponds to the highest intensity, which could either be the 53 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. window, or a patch of light on the wall above the monitor or a patch of sunlight on the floor. By identifying the surface which is at the highest intensity, we can then evaluate its importance in the field of view of the occupant, and whether it could be a potential glare source. The image also shows us the occupant’s interaction with the visual environment. The position of blinds, and obvious change of task location or any other occupant response can also be studied from these images. 5.6 Observations A few representative cases of the data obtained at the Collins Center are discussed below. Please refer to Appendix A for a discussion of the remaining tests and observations. March 27,3:00 p.m., Room 1 The histogram shows a uniform bell curve with a peak at the high intensity corresponding to that of the window as observed from the image (Fig. 5.3). The known luminance box is in the 128-160 relative range on the histogram, which sets the absolute range from 0-406 fL. The wall behind the monitor is at a higher luminance than the rest of the space as more light bounces off from the lightshelves into the room and onto the walls. 54 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. :e"“ * « « r i b ution ^ 27. 3:00 55 ReProducedw i , With P e rm ,s s ^ 0 f ll)e pmh'blt^ tK rm lss^ The image shows no other high intensity regions in the field of view other than the window. There is no internal glare within the room. There is internal glare within the camera’s field of view which is caused as a result of the bright window sill and jamb. The rest of the space is more or less uniform in light distribution. The histogram shows a smooth wide histogram depicting a uniform distribution of intensities across the room. The spike at the higher intensity corresponds to that o f the window, and may or may not cause discomfort depending on occupant location and task location. March 27. 5:00 p.m., Room 1 The known luminance box is in the 96-128 relative range of intensity, with the window sill and lightshelf at the highest intensity of 522 fL absolute (Fig. 5.4). The area of highest intensity is the window sill, light shelf and a few areas on the work surface. The contrast between the high intensity and the background is higher than that of the 3 p.m. distribution as a result of the lower background levels as well as the higher window luminance. The wall within the field of view of the occupant is brighter than the rest of the space with a few patches of direct light hitting the work surface which could cause discomfort. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with March 27,5;00pm, Room 1 22000 20000 18000 18000 i E 3 % 10000 8000 6000 4000 2000 108 118 127 138 145 154 Intensity 163 172 181 190 195 2CS 217 226 235 244 253 Fig. 5.4.1 Histogram o f Intensity Distribution Fig. S.4 March 27, 5:00 p.m., Room i 57 permission of,he oopyrigh, owner. Further reproduotion prohM ed without permission: April 5,5:00 p.m. Room 1 The known luminance box is in the 160-192 relative range on the histogram. The absolute value of the brightest pixels is therefore 360 fL. The window sill and table along the far opposite comer of the room are at the highest intensity and correspond to the spike at the high end of the histogram (Fig. 5.5). The bell curve is tall and narrow, signifying low background luminance levels and greater contrast, which is confirmed by the image. This causes extreme discomfort within the space. The blinds were let down over the top portion of the window, to cut out the direct sunlight, as a means to reduce the discomfort. There was and still is internal glare within the room, caused by the excessive brightness of the wall compared to the desk surface and monitor or the contrast between the papers on the desk on the far side of the room compared to the rest of the background. The window sill would cause discomfort if it was within the field of view of the occupant. As such there is plenty of internal glare caused due to high contrast between background and areas of excessive brightness. April 5,5:00 p.m., Room 2 The known luminance box is in the 224-256 relative range on the histogram. The portion of the window seen beneath the blinds and table tops are at the highest intensity of 250 fL. The spike on the left side of the histogram corresponds to the low background Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. April 5 ,5:00pm, Room 22000 20000 16000 16000 —___ * 14000 J - a £ 12000 • o J§ 10000 ■ --------- 6000 o o o o 4000 2000 100 109 118 127 136 145 Intensity 19fl 206 217 226 23S 244 253 Fig. 5.5.1 Histogram o f Intensity Distribution A p rils, 5:00pm, Room 2 Reproduced with 22000 20000 18000 16000 i E a Z 8000 6000 4000 2000 10 19 91 1 °° 1 0 9 1 1 8 ’ 3 8 , 4 5 , 5 4 , 8 3 , 7 2 ,8 , Intensity 190 189 2 0 8 2 1 7 226 23 5 244 2 5 3 Kg. 5.6.1 Histogram o f Intensity Distribution Kg. 5.6.2 K g. 5.6 April 5, 5:00 p.m., Room 2 6 0 permission of the copyright owner. Further reproduction prohibited without permission. level (Fig. 5.6). Glare is caused as a result of direct light into the room and is partly corrected by letting down the blinds. If the blinds were let down completely, the remaining high luminance pixels would disappear and the histogram would contain just the bell curve and the spike at the lower intensities. October 2,12:00 noon, Room 1 The known luminance box is in the 224-256 relative range on the histogram. The window and the known luminance box are at the highest intensity, corresponding to the spike at the right end of the histogram (Fig. 5.7). The bell curve is tall and narrow, distinctly separate from the spike and hence the likelihood of causing glare is high. The predominant background level is low. The wall behind the monitors is graded into the high luminance of the window. The glare is not internal, in that there is no high contrast between surfaces within the room. The highest intensity is that of the window. The glare would be caused because of the contrast between the window and the background. Hence an actual feeling of discomfort will depend on where the occupant performs his task and whether the window forms a part of the field of view. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. October 2 ,12:00pm, Room 1 22000 • 10000 ■ 8000 ■ 4 ................................................................... 0000 ■ ■ i- i- i- iv iv i- i- iv l- : ': I - 4000 ■ f t I 2000 • 0 ■ I l .I ! . I . I l ! 1 10 19 2$ 37 46 SS 64 73 82 91 100 109 118 127 138 145 154 183 172 181 190 199 208 217 226 235 244 253 Intensity Fig. 5.7.1 Histogram of Intensity Distribution Fig. 5.7.2 Recorded Image Fig. 5.7 October 2, 12:00 p.m., Room 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Relation between the histogram and the background luminance The wider the curve of the histogram, the greater the number o f luminance levels present in the room, which is better than sharp spikes corresponding to sharp changes in the luminance of the background. A tall narrow curve with sharp spikes and a wide separation between the curve and the high intensity spike is very likely to be a glare situation. The middle range on the histograms, that is the distribution between the bell curve and high intensity peak is probably the distribution along the wall surfaces. Absence of any significant number of pixels in this region implies a lesser distribution of intensities within the space. The higher the number of pixels in this region or the beginnings of another curve show that there is an uniform distribution along the surface and less likelihood of causing a glare. October 2,12:00 noon, Room 2 The known luminance box is in the 224-256 relative range on the histogram. The window, known luminance box and table surface are the highest intensity of 240 fL. The histogram shows pixels at almost all intensities, with a smooth bell curve and a spike at the right high intensity region (Fig. 5.8). The general background level is higher and hence there is less possibility of the high intensity causing glare. The wall behind the monitors also is graded in its intensity and this is confirmed by the presence of pixels in the range between the bell curve and the spike. 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ens,ty Distributi h o r d e d I, 6 4 Reprodi u c e d with Permission o f the c°Pyright owner' F w h e r reProductiori Pr°hibited without Permission. 5.7 Conclusions 1. The method seems to be applicable from a numerical standpoint by analyzing the histograms. The histogram is capable of establishing the background level or the adaptation level within the space, the percentage of field of view that the glare source and the background occupy, as well as the absolute values of intensities within the space and contrast of highest luminance with that of the background level. 2. The image makes it possible to define which surface has the highest intensity, and establish the range of absolute intensities within the space. It also gives a record of the window blind positions and any interaction of the occupant with the visual environment. 3. There is, however no way to find out if the blinds were down as a result of visual discomfort at that particular instance or were in that position since some other situation previously experienced. These observations need to be tested against a large number of individuals occupying that space to determine their reaction to that situation or the position of the blinds must be periodically reset. 4. The position of the camera is another critical factor in the method. These observations have been made with the entire space in the field of view. However, there are other locations which are more interesting. The camera can be placed to mimic an occupant at his/her task location, either reading at a desk, looking at a computer screen etc. This information, although valuable, might prove to be difficult to obtain since in a real life Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. situation the space is occupied by the occupant. This brings up the suggestion of setting up a test cell. 5. It is necessary to obtain occupant observations and evaluations in the form of surveys or questionnaires to back up the numerical analysis and conclusions. Since glare is such a subjective phenomena it is essential to reinforce numerical data with subjective impressions of which ratios and percentages of view cause glare, and which are acceptable. 6. The critical factor determined from the histograms is the ratio of the extreme intensity to the median of the background intensity. There are actual intensity levels exceeding 1:250 within the space, but the ratio of highest intensity to that of background intensity is more crucial in determining glare conditions. From the histograms it is found out that a ratio of 3:1 or greater begins to feel uncomfortable. Any ratio of 4:1 or greater positively produces a sensation of discomfort and should be avoided. 7. To further analyze the glare response of occupants within the space, a test cell would have to be set up, where exact luminances corresponding to specific ratios of background to extreme can be produced and tested with occupants being surveyed while being exposed to those controlled visual conditions. These conditions can be videotaped and digitized for later numerical analysis. The occupants would be surveyed simultaneously as the test progresses. Specific ratios of background to extreme and field of view can be tested to find conditions of visual comfort and glare response. 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.0 TESTING THE METHOD Based on the conclusions from the earlier study, the necessity to set up a test cell to further evaluate and test the method was identified. The space chosen for the test was HAR210 at the University of Southern California. The purpose of the test cell was to be able to simulate different luminances and contrast ratios within a space, while occupants were being surveyed simultaneously for their response and interaction to those visual conditions within the space. Along with recording luminance variations within the space, protocols for capturing images, data transfer and analysis were also laid down. 6.1 Design of the experiment A single rectangular aperture 4ft x 2.5 ft (1200 x 750 mm) was used to test various contrasts between the source and background luminance. The top half of the window was boarded up with opaque material, so as to block out the light. The lower half of the window was boarded with papers of different transmissivities, so as to simulate different luminances. The background level was changed by turning the lights on and off. The known luminance box was placed in the image to set the range of intensities within the space. The images were recorded for various contrasts between window luminance and background. A total of six occupants were surveyed. The recorded images were converted into histograms of intensity distributions, and a similar 67 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. method of analysis was followed as in the earlier method. (Please refer Chapter 5 for the analysis procedure.) 6.1.1 Location of the camera The camera was positioned facing the window, simulating an occupant’s field of view. This position was kept constant in all the experiments conducted. 6.1.2 Location of the box The known luminance box was placed on a shelf below the window, so that it is not affected by light coming in from the window. This sets the absolute range of intensities within the space. 6.2 Description of Equipment 6.2.1. JVC Camera A JVC GR-M73 9 Camera Recorder with time exposure capability was used for the experiment. The camera is equipped with a nickel cadmium battery which is connected to the AC outlet through an AC power Adapter/Battery Charger AA-V10U. Any other model of a camera-recorder can be used, but the compatibility of different types of video format and input connections between the camera, video board (computer), and software for later downloading and analysis had to be looked into, for 3 9 JVC GR-M7, Camera-Recorder/Playcr Instruction Manual. 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. example NTSC, PAL, VHS, Super-VHS, Beta and 8 mm formats and composite and serial port connections. 6.2.2 Compact VHS-C tapes Compact VHS-C cassette tapes were used to record the images. If some different type of camera is used, compatibility of tape and camera will need to be determined. 6.2.3 Luminance Box The same luminance box as described in section 5.2.2 was used in this experiment. Please refer the section for further details. 6.3 Testing and Recording There were six variations of contrast conditions between the high intensity and background being tested with each occupant. The date time function on the camera was turned on so that there was an inbuilt record of the observation. Since the occupant was being recorded simultaneously with the luminance variations in the space, correlating recordings to each occupant and their response was made easy with an in built recording of the date and time. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.4 Occupant Survey The questions in the occupant survey address the perceptual responses of the individuals in an experimental setting, at an experimental task. For each setting the occupant was asked to answer the full set of questions about the contrast ratios, brightness and glare within the setting. The response was scaled on a scale of 1-5 with 5 being on the high end and 1 signifying the low end (Fig. 6.1). How'would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Scaling 5 4 3 2 1 Fig. 6.1 Example of Rating scale An example of the survey is included in Appendix B. The occupant was asked to respond to the survey questions while the space was being simultaneously recorded. Response to each experimental setting was then correlated to the recording, and the digitized information about the luminance ratios and contrasts within the space. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.5 Capturing the video images The captured video images were then digitized. An IBM-PC 80486 was used with a video digitizer board within the PC to digitize the images. Video for Windows4 0 was the software used to edit and capture images. The video output port of the camera is connected to the video-in port of the PC. The cassette is replayed and images are captured while being displayed on the screen. The preview mode was used to replay the cassette and capture the exact frame needed. Some images were more clear and stable than others. Depending on the software used to capture the images, the resolution of the acquired video image changes. A video format of 16.8 million colors was used. As the video is replayed, each selected image was captured. The image needs to be given a filename and an extension. The images can be saved as different file types like a *.BMP, *.PCX or any other extension offered by the software. The .PCX format was used since it is universally acceptable. The next step was to convert this binary file to an ASCII data file. This can be done in many ways. There are conversion utilities available which convert binary data to ASCII data. The UNIX based utilities called the ‘pcxtoppm’, ‘tiftoppm’, ‘giftoppm’ etc. were used to convert the data. This generates a .PPM file which holds the ASCII data, corresponding to the luminance value of each pixel in the image. 4 0 Video for Windows software registered with Microsoft 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These .PPM files were then converted to .XLS format which is acceptable by any spreadsheet program, for example EXCEL, using the software VIDEO4 1 which was developed at the California Polytechnic Institute at Pomona to generate a .XLS file which gives the intensity of each pixel on a scale of 0-255. 6.6 Gathering Data The digitized images showed specific cases of high contrast as well as luminance variations across the space. The images vary from setting to setting depending on which paper covered the window, the luminance of the sky outside and whether the lights were turned on or off within the space. A written survey was completed by each occupant based on their response to the light distributions within the space. The histograms of the images conveyed information about the relative range of intensities, percentage of field of view as well as well as the contrast ratios within the space. 6.7 Analysis The collected data was analyzed in the same manner as discussed in Chapter 5. The collected data was analyzed in terms of 1. Histograms of the intensity distributions within the space and 2. Recorded images of the space (Fig. 6.2). 4 1 Video was developed at the California Polytechnic Institute. 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Numerical Analysis of Histograms NAME MEDIAN WEIGHTED NO.OF TOTAL % VIEW MAX INT RATIO RATIO NO. OF % VIEW GLARE ANALYSIS PIXEL INT AV. INT. B,PIXELS PIXELS MAX.INT Imp Iw lm Im/Imn Imflw PIXELS = April. 1.8:4?. .......... 80: 81.76; 64920: 76800; 84.50%: ........254!..............3;2!....... ........3,1:...... 5429; 7.10% GLARE : April 1,8:38 am ] 82: '78.82': 65981! 76806: " '85.96%';' 254: 3.1; 3.2: 7291: 9.50% "NO GLARE ' ■ A pril 1,6:48 ani......... ............78: 77.35: ''"63395]'" " 76866:" ' '8250% ;' ..... 254';' ' ..... 3 3 ]...... .......3 3 ; ....... .......6944":..... " '9.6d%lPR6*BABLE" March 28,8:35 am 73: 74.07; 615041 76800; 80.10%] 254: 3.5 ; 3.4: 7748! 10.10% GLARE :March30,9:31 am 70: 71.49; 57610! 76800: 75%] 254: 3.6! 3.6; 7446: 9.70% GLARE march 30,9:44 am 70, 70.25; 56839] 76800; 74. 00%; 254, 3 6 , 3 6 , 7744: 10.10%:GLARE •March 30,9:39 am \ 68: 68.8: 52628': 76800: 88.50%] 254: 3.7: 3.7! 7914: 10.30%NO GLARE March 30,9:50 am 71 i 68.22: 56469] 76600: 73.50%: 254, 3.6; 3.7! 7569! 9.90%’PROBABLE :foarcn 28,8:22 am ] 69: 68.06: 57410! 76800: 74.80%] 254: 3.7: 3.7: 6758; 8.80%:PROBABLE jMarch.28,.8:Mam..... .............69; 68.07: 58250] 76800: 75.80%; March 30,9:27 am ;Marcli 28,8.19 am 64: 68: 67.7: 87.1; 62048: 56954] 76800= 76800: 74.20%i • 254, 3 7 , 3 8 , 7932! 10.30% 'GLARE !March 28,8:31 am ] 68.5: 66.97: 55882: 76800! 72.80%] 254: 3.7! 3.8: 7840: 10.20%NO GLARE !March28,8:41 am 67.5; 65.85: 57429] 76800: 74.80%; 254, 3.8! 3.9; 7413! 9.70% ’PROBABLE :March 28,8:49 am ] 65: 64.58: 57284; 76800! 74.60%] 254: 3.9: 3.9: 6110: 8.00% PROBABLE IMarch 28,8:11 am 64: 62.94: 52283] 76800: 68.10%: 254 4 0 , no, 8573; 11.20% PROBABLE ;March28,9:01 am : 65.5: 62.79; 59304] 76800: 77.20%: 254; 3 9; 41; 5667! 7.40% PROBABLE March 28,8:56 am ■ 59: 60.38: 51363: 76800: 66.90%] 254! 4.3: 4.2: 8570: 11.20% GLARE March 30,9:46 am 62: 59.99: 55055] 76800: 71.70%; 254, 4 1 , 4 2 , 8367! 10.90%‘GLARE .-March 28,8:38 am ; 56: 56.28; 53195! 76800; 69.30%] 254! 4.5: 4.5: 8314; 10.80% ;GLARE :March 28,8:24 am ; 52.5: 54.28: 57726: 76800! 752; 254! 4.8! 4 7 6160: 8.00% GLARE March 30,9:18 am 54.5 : 52.78: 55626] 76866: 72.40%; 254, 4 7 , 4 8, 6691; 8.71% NO GLARE March 28,8:50 am ■ 53: 52.26: 55221; 76800: 71.80%] 254: 4.8: 4.9: 6263: 8.20% PROBABLE March 30,9:34 am 5 3: 52.19; 54131! 76866: 70.50%: 254, 4 8 , 4 9 , 6108: 10.60% GLARE March 28,8.42 am ■ 53; 51.8: 56184; 76800: 73.20%] 254: 4.8: 4.9: 7428: 9.70% GLARE March 28,8:32 am 54.5; 51.38: 54030! 76806: 70.40%: '254, 4.7! 4 9 , 8065! 10.50%’PROBABLE :March 28,9:03 am ■ 51; 50.85: 52947: 76800: 68.90%: 254: 5.0! 5.0: 8322! 10.80%GLARE : March 30,9.52 am....! _ .............52:..... ......49.38":...... ......52468!.... .....76800':.... ... 68:26% ]..... .......254:....... ......4i9i................5/ 1 ":..............7368:"" .... SM % :OU«E....... iMarch 26,6:13 am 51: ..... 4 9 . C i 3 :...... 56914] 76866:" 74.i'6%!...... I " .2 5 4 ] '] ' .....* '5*.6';**"'* ■ 5.2 V ...... ....... 5' 9'3 'i"!..... "'"7.7d%:GLARE......... lApnl 1,8:44 am ■ 44: 48.38: 56291! 76800; 73.30%] 254: 5.8: 5.3 ; 6866: 8.90% GLARE iMarch 30,9:41 am 46 i 46.79: 53038] 76800: 69.10%: 254, 5 5 , 5 4 , 7732; 10.10% ’g l a r e ! April 1,8:39 am ; 44: 46.46; 53881! 76800; 70.20%: 254: 5.8: 5.5 ; 6690: 8.70% GLARE iMarch 30,9:21 am..... 45; 45.18; 54228; 76800'; 70.60%: 254! ..... 5.6:..... 5.0 : 8361: 10.90% GLARE :April i , 8:49 am.......... ,.'.]5 3 M 9 T ]....tesoo:'".' Z M m C Z 254;.:.... ....Is& Q ...Z3K:."..ZZjM lZ ...."9i6%;roOBABLE" Fig. 6,2 Numerical Analysis of Histograms 3. Occupant survey. The observations were based on the histograms, images as well as occupant response. The histogram and image analysis was carried out as before. 6.7.1 Analysis of Occupant Response The response analysis was carried out for specific ranges of contrast ratios of 3.1-3.5, 3.6-4.0, 4.1-4.5, 4.6-5.0 and 5.0-5.6 between the high intensity and the background level within the space. The verbal response of the occupants to questions about the visual environment was scaled from 1-10. A scaled response of 10 meant that the space was extremely bright, glary and uncomfortable and 1 signified that the space was visually comfortable with lower contrasts and better distribution (Fig. 6.3). O C C U P A N T R E S P O N S E 3.6-4.0 4.1-4.5 4.6-5.0 C o n tra st R atio betw een High Intensity and B ackground BD egreeof Discomfort (Scale 1 to 10) OContrast Between Window and Background (Scale 1 to 10) ■ Contrast Between Window and Surround (Scale 1 to 10} Fig. 6.3 Occupant Response 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.8 Observations A few representative cases of the experimental settings are discussed here. Please refer to Appendix C for further observations and discussion of test settings. March 28, 8:11 a.m. The histogram does not show a uniform and distinct bell curve. However the background shows a distribution along the low intensity range and a tall spike at the high intensity. The known luminance box is in the 160-192 range on the histogram, which assigns an absolute luminance value o f370-400 fL to the window. The wall around the window is not graded in intensity. This is seen on the histogram in the lack of pixels between the bell curve and spike (Fig. 6.4). The window is at the highest intensity. The predominant background level is 100 fL, and this contrast of low background with the high intensity window causes the discomfort within the space. The contrast between the window and background is around 4:1. The occupant judged the glare from the window to be uncomfortable, with high contrast betweend the window and surround, and the brightness of the source to be very high in comparison with the brightness of the rest of the space. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner f , ,r+ ho Wner' FUrther reP ^ u c tio n prohibited without permission. March 28, 8:24 a.m. The bell curve is narrow which signifies a lesser distribution of intensities across the space. The bell curve is also shifted towards the left indicating lower background levels. The window is the region of highest intensity and is represented by the spike on the histogram (Fig. 6.5). The known luminance box is in the 192-224 range on the histogram which places the window at 310 fL. The contrast between the window and surrounds is high. There is no grading of intensities across the wall as seen from the image. The contrast between the high intensity source and background is 4.6 and above. This contrast definitely produces discomfort. Occupant response to the lighting conditions within the space was, high contrast between window and surround, with glare from the window which is however not very uncomfortable. The brightness of the source was not higher than that of the rest of the space. March 28, 8:49 a.m. The known luminance box is in the 160-192 range on the histogram. Hence the absolute range of intensities within the space is 360 fL, with the window at the highest intensity. The bell curve is wide, setting a background level of 65 (relative) on the histogram (Fig. 6.6). The contrast between the window and the background is 3.9. There will not be excessive discomfort felt within the space, as there is come grading of intensities across the wall next to the window. This reduces the discomfort of the 77 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 118 W ,3( Wtensity Histogram ■ nsity Distribute; Pt8. 6.5.2 Recorded h Fig‘ 6.5 March 28 jm 78 Fig. 6.6 March 28, 8:49 a.m. 79 excessively bright window in comparison with the background. The occupant response to the contrast ratio between the window and the surround was ‘not high’, there was glare from the window which was uncomfortable and the source was brighter than the brightness of the room. March 28, 8:54 a.m. The histogram distribution is spread out, but shifted towards the lower intensities. The known luminance box is in the 160-224 range on the histogram, which sets theabsolute range of intensities within the space to 0-390 fL. The contrast between the window (area o f highest intensity) and the adaptation level in the space is 4.1. The brightness of the window in comparison to the low background levels causes the discomfort within the space (Fig. 6.7). The occupant felt that there was glare from the window which was not uncomfortable, and there was not much contrast between the window and its surrounds, while the source was brighter than the room. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 28, 8:54am 9000 8000 7000 6000 £ s £ 5000 *5 4000 3000 2000 1000 ■ fl, J it 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 172 181 190 199 208 217 235 244 226 253 Intensity Fig. 6.7.1 Histogram of Intensity Distribution Fig. 6.7.2 Recorded Image Fig. 6.7 March 28, 8:54 a.m. 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. April 1, 8:38 a.m. The bell curve distribution on the histogram is wide and tall. The window is still at the highest intensity of 250 fL, since the known luminance box is in the 224-250 range on the histogram (Fig. 6.8). There is a spike, but the contrast between the window and adaptation level is 3.1. The lowering in absolute values of luminances can be put down to it being a cloudy day. From the image it is seen that there would not be any discomfort felt in such a space. The occupant said there was not much contrast between the window luminance and its surround. There was no glare from the window with the space being comfortable, and the brightness of the source almost equal to the brightness of the room. April 1, 8:39 a.m. The bell curve is still wide, but the peak of the bell curve is moved towards the lower intensities indicating that the background or adaptation level is lowered further. The spike at the right end of the histogram still represents the window as it is the area of highest intensity in the image (Fig. 6.9). The known luminance box is of the highest intensity, i.e. it is in the 224-256 range on the histogram. There is extreme contrast between the window and background. This high contrast causes the discomfort in the space. The occupant said there was high contrast between the window and its surround, with glare from the window which was uncomfortable and the source was brighter than the room. 82 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. !nsityDistrib, ^corded h P nU 8:381 83 e m issio n o f„, vy ignt owner ForthD APril 1, 8:39am 9000 5000 7000 6000 £ 5000 3000 2000 — - 9 208 2 (7 228 238 244 283 '0 0 109 118 127 136 148 184 Intensity 163 172 101 1 9 0 199 F‘S' 6 9 1 Hist0gram ° f Intensity Distribution Reproduced with permission of the copyright owner. Further reproducf h reproduction prohibited without permission. 6.9 CONCLUSIONS 1. The method is numerically defined, and protocols for recording, downloading and converting data are established. 2. Occupant response was correlated with the data and it confirmed observations made from the histogram and image analysis in most of the cases. It was found that there was 100% concurrence among all the occupants that a contrast ratio of 4.1-4.5 between the high intensity and background will cause glare. There was a 75% concurrence among the six occupants that a glare ratio of 3.6-4.0 and 4.6-5.0 would cause glare (Fig. 6.10). OCCUPANT RESPONSE * S 1 0 0 % I............ W ... ......I ffi 90% 3.1- 3.6- 4.1- 4.6- 5.1- 3.5 4.0 4.5 5.0 5.6 Contrast Ratio betw een High Intensity and Background EG lare yes BGlare no Fig. 6.10 Occupant Response to Contrast Ratio between High Intensity and Background. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. For a contrast ratio of 3.1-3.5, there were 50% of the occupants felt that the space was glary, and 50% who felt that it was not glary. Since glare is a subjective phenomenon, and at that high contrast level, the distinction between glare and no glare becomes thin, subjectivism plays a greater role. From the occupant analysis it was also found that at high contrasts, the difference between occupant response was high. 40% of the occupants said that a contrast ratio of 5.1-5.6 did not cause glare. By examining which setting resulted in these contrast ratios, it was found that by the time the occupant reached the sixth experimental setting, he was getting adapted to the high intensity and contrasts within the space. This is a probable reason why such a high contrast would not seem to cause glare to a few of the occupants. This brings up the question of setting up a completely controlled test cell, where the occupant is not given a chance to get adapted to the high intensities within the space. The small number of occupants surveyed causes a greater deviation in their response. A test cell with more experimental settings and a larger number of occupants surveyed should be conducted to be able to draw conclusions and deviations necessary to establish the method. The experiments should also be conducted in random order between the levels being tested or there should be a reset period between the tests so that the occupants are not exposed to the high contrasts continuously. 3. The limitation while testing the method was soon found to be the test cell itself. There was extraneous light within the image from the space around, and hence the histogram distributions were not so pronounced. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. Due to the lack of pronounced histogram distributions, it becomes difficult to establish the extent of the bell curve or level of the background intensity within the space. 5. To effectively discuss histogram distributions, a completely controlled test cell would have to be set up where luminances of background and source are controlled and there is no extraneous light entering the cell. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.0 RECOMMENDATIONS AND FURTHER WORK 7.1 Conclusions This thesis has been completed to demonstrate the workability of a new method for glare analysis. We recognize that this is a new method of measuring luminances and contrast ratios within a space, with an aim to understand glare behavior. An understanding of the glare phenomenon and a method to measure it, will encourage the use of this method in order to control glare and visual discomfort in buildings, whereby minimizing building operations costs by saving energy. Furthermore, buildings can be created based on visual comfort considerations rather than solely on light level considerations and in the process create better living spaces in the future. The method is established numerically and is capable of developing a method for analyzing glare behavior in spaces. The method is simple, and much less tedious than manual methods. The great advantage of this method is that data is obtained in great detail from a seemingly simple experiment. This is made possible by the use of video photometry in conjunction with the capabilities of the computer to store and handle great amounts of data. The method is powerful and flexible. It can be used by an architect or designer to quickly analyze the luminance distributions within the designed space or it can be used for empirical research where data corresponding to approximately 125,000 luminance meters placed in the space is obtained. This is by no means meager data. It depends on what you want to analyze out of the data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Protocols for recording, downloading and converting data are also established. While using the method to determine glare behavior and its causes, it was found that the method seemed to have some shortcomings, as was discussed in the conclusions following the experiments. There was extraneous light within the experimental space, which effected the histogram distribution making them less pronounced. This can be avoided by setting up a test cell where the source luminance, and background luminance are controlled. Also the number of occupants surveyed was six, and hence the percentage weightage given to each response was high. This increased the possibilities of high deviations in occupant response. A larger number of occupants can be tested for a greater number of experimental settings, to get a wide database of information over which the method can be developed further. 7.2 Recommendations To determine baseline glare ratios, it is necessary to repeat the experiment within a test cell which is completely controlled. Also, a greater number of occupants should be tested within the test cell, exposed to a wider range of contrast ratios between the high intensity and background levels. It is also proposed that this method be used as a teaching tool to demonstrate the concepts of visual comfort, luminance variations and glare to students in the classroom. Not only is the method easy to demonstrate and work with, it also introduces the students to data collection and figuring out what to do with the enormous amount of data the computer is capable of generating. This method is also fairly simple to use in the design arena directly, where designers can quickly analyze the 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. luminance distributions within the created space and find out if they would cause discomfort. The method would be more useful in predicting glare behavior in building energy simulations such as DOE than current algorithms. This method could also be useful for post occupancy building analysis. Any significant area can be examined and monitored along with the subjective impressions of the occupant, and can provide useful information in understanding the glare response of occupants. There is a lot of potential in the method to understand glare behavior. However, to establish itself as a recognized method for glare analysis, it will have to undergo extensive testing for verification. With rigorous testing and greater number of experiments, a comprehensive method for glare analysis could be laid down. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A - OBSERVATIONS A.1 Observations This is a discussion of the tests and data obtained at the Collins Center. Please refer Chapter 5 for further analysis and conclusions. March 27,3:00 p.m., Room 2 The luminance box is in the 128*160 relative range on the histogram. The window, parts of the table top near the window and the wall behind the monitor are at the highest luminance. The histogram shows a distinct spike on the left which corresponds to all the dark spaces within the room (Fig. A.1). The bell curve shows up after this spike, along with another distinct spike at the high intensity. The contrast ratio is high (3.97) between the high intensity and the background. There is some internal glare within the room, as there is high contrast in the field of view of the occupant at his task location, i.e. contrast between the table top, monitor screen and the wall behind the monitor which is excessively bright. March 27,5:00 p.m., Room 2 The known luminance box is in the range of 96-128. The window sill and a few patches of direct sunlight on the table and the wall perpendicular to the window are at the highest intensity (Fig. A.2). The histogram shows a very wide bell curve, with pixels at 91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. A.1 March 27, 3:00 p.m.. Room 2 92 Reproduced with permisslon of the r reproduction prohibited without permission. 22000 March 27,5:00pm, Room 2 20000 18000 16000 m 14000 12000 10000 8000 6000 4000 2000 1 10 10 28 37 46 55 64 73 82 91 100 109 118 127 138 145 154 163 172 181 190 199 208 217 226 235 244 253 Intensity Fig. A.2.1 Histogram of Intensity Distribution Fig. A.2 March 27, 5:00 p.m., Room 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. all intensities. The sharp spike at the left indicates the dark areas in the background. Even though the contrast is much higher than that at 3:00 p.m., it would not cause discomfort, because of the uniform distribution of intensities across the space. There is another bell curve between the bell curve representing the background and the high intensity spike. This represents the intensity distribution along the wall surfaces. This is almost an ideal distribution within the space. April 5,3:00 p.m., Room 1 The known luminance box is in the 160-192 relative range on the histogram. The window and the wall adjacent to the window are at the highest absolute intensity and are represented by the spike at the high intensity on the histogram (Fig. A.3). The bell curve is narrow and located on the lower intensity areas. From the image, it is obvious that the entire room is at a low background level, and hence there is a high contrast between the background level and high intensity. Based on the histogram, this distribution is likely to cause glare, especially when there is distinct right spike, which represents areas of high intensity within the space. From the image it can be seen that the wall behind the monitor is excessively bright and could be a source of glare along with the window. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. A.3 April 5, 3.00 p.m., Room] 95 Reproduced whb p e n s io n of the reproduction prohibited without permission. April 5,3:00 p.m., Room 2 The histogram seems to be incomplete, skewed or improperly scaled. From the image it is seen that there was direct sunlight pouring in through the window. The window, wall surface near the window, table top and floor near the window are flooded with direct light (Fig. A.4). The rest of the room is at a comparatively low background level and the space is likely to feel uncomfortable. The top o f the blinds have been let down to shut off some of the direct light into the room. October 2,9:00 am, Room 1 The known luminance box is in the 224-256 range on the histogram. The known luminance box, window and some patches on the wall behind the monitor are at the highest intensity (Fig. A.5). The background level is low as seen from the histogram distribution. There is a possibility of internal glare as there is a high contrast between the computer screens and the wall behind them. The histogram distribution shows a tall narrow curve with prominent spikes representing the low levels of the background. The spike at the high intensity represents that of the window and luminance box. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. April 5, 3:00 pm, R o o m ; 16000 I? 10000 E 1 1 0 1 0 • * » . ’ 9 28 37 « 5 5 „ % - A.4.1 Histogram o f Intensity Distribute 73 52 81 100 10® 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 Intensity ution Fig. A.4.2 Fjg. A.4 April 5, 3;oo Recorded Image Pro., Room 2 97 Reproduced with Permission of the copyright owner. Further reproduction Prohibited without permission. O ctober 2 ,9:00am, Room 1 22000 2 0 0 0 0 18000 16000 rt 14000 £ 12000 & 10000 8000 6000 4000 2000 ■ ■ & ■ » ■ ■ ■ ! i.irii t U i ,„ J I H ,lj « JLfc, I t l lUl I , fo I.IU .U,.. * < ■ -1 ■ ■ ■ » ■ A.Jj 1 10 19 28 37 46 55 64 73 82 01 100 109 118 127 136 145 154 163 172 181 190 Intensity 199 206 217 226 235 244 253 Fig. A.5.1 Histogram of Intensity Distribution Fig. A.5 October 2, 9:00 am, Room 1 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. October 2, 9:00 am, Room 2 The known box is in the 224-256 range on the histogram. The known luminance box, window and patches of light on the desk top are at the highest intensity of 250 fl. absolute. Even though the entire window is at a high luminance, there may be no actual feeling of discomfort because of the high values of background luminance present in the space. The work surface is also at a high luminance. The wall behind the monitors is graded uniformly, with the highest values closer to the window. This gradation reduces the possibility of glare within a space. The bell curve shows pixels at all intensities with the right spike indicating the window and known luminance box (Fig. A.6). This distribution across the histogram is less likely to cause discomfort within the space. October 2,3:00 p.m., Room 1 The known luminance box is in the 224-2 56 range on the histogram. The highest absolute intensity corresponding to that of the window and the known luminance box is 240 fl. The desk top and wall behind the monitor is at a higher intensity than the rest of the space. The histogram distribution shows a tall narrow curve at the low intensity levels and a high intensity spike corresponding to that of the window and the known luminance (Fig. A.7). There is no glare within the room, since the wall surface is considerably brighter than the rest of the room. The high contrast is between the window and the background. The window will be a source of glare if it is within the field of view of the occupant. 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproc/ October 2.3:00pm, Room 22000 20000 16000 14000 12000 10000 8000 0 0 0 0 2000 H e. A.7.1 Histogram o f Im enstV restribution'’” ""”' 172 1*1 190 199 208 2 1 2 228 235 244 253 F,g‘ A'7 0ctober 2. 3-00 p . m . , R o o m j > V a». Recorded Image 101 Reproduced with permission of the copyright owner" f,,„ h ' ' ...... ................... PV tgh. owner. Further reproduction prohibited without permission. October 2,3:00 p.m., Room 2 The known luminance box is still in the 224-250 range, setting the absolute range to 0-250 fl. The window, known luminance box and patches of direct sunlight on the floor are at the highest luminance. The space is at a higher background luminance than that in room 1. The desktops and walls are considerably brighter than the rest of the room. The histogram shows a uniform wide bell curve with a spike at the high intensity corresponding to that of the window, and known luminance box (Fig. A. 8). The possibility of visual discomfort being experienced is less, as seen from the image and distribution. October 2, 6:00 p.m., Room 1 The situation in room 1 seems to have improved with the background level increasing considerably. The known luminance box is in the range of 224-256 range on the histogram. The window, lightshelf, and the known luminance box are at the highest intensity o f 250 fl. The histogram shows a narrow tall curve with the high intensity spike (Fig. A. 9). There is another distribution between the tall curve and the spike. This reduces the possibility of a glare situation as discussed earlier. Examining the image shows that the wall surfaces are pretty evenly graded and would not cause any discomfort. Although the contrast between high intensity and background is high, the position of the high intensity areas in the window are critical. Hence there is no discomfort felt in the space. 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with October 2, 3:00pm, Room ; 19000 •5 1 0 0 0 0 37 46 55 64 73 62 91 100 108 116 127 136 145 154 163 172 181 190 199 206 217 226 235 244 253 Intensity Fig. A.8.1 H istogram o f Intensity Distribution -, ' v v ' ' W , . ' ' % - A f e ; ' ,■ * ' ^ « •:; -V' ^ * „ ' " v - ... ' ,v s.. i — m r Fig. A. 8.2 Recorded Image Fig. A.8 October 2, 3:00 p.m., Room 2 103 Permission of the copyright owner. Further reproduce reproduction prohibited without permission. October 2 ,6:00pm, Room 1 12000 & 10000 e z 8000 r r h r ■ t i - U ■ t J * ^ L 1 10 19 28 37 46 55 84 73 82 01 100 109 118 127 138 145 154 183 172 181 190 199 208 217 228 235 244 253 Intensity Fig. A.9.1 Histogram of Intensity Distribution Fig. A.9.2 Recorded Image Fig. A.9 October 2, 6:00 p.m., Room 1 104 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. October 2, 6:00 p.m., Room 2 The known luminance box is in the 224-256 range on the histogram. The window and known luminance box and a few patches on the desktop are at the high intensity of 250 fl. The background levels are much higher and hence the contrast between the high intensity and background is lower. The wall behind the monitor is uniformly graded in intensity. The histogram shows a wide bell curve with higher background levels (as seen in the shift of the curve towards the right), a high intensity spike corresponding to that of the window (Fig. A. 10). The pixels at the intermediate intensities represent the grading of the wall surfaces. This sort of distribution is ideal and has no probability of causing glare. December 21,1:00 p.m., Room 1 The known luminance box is located in the 224-256 range of intensities on the histogram. The window and known luminance box are the surfaces at the highest intensity. The histogram distribution shows a wide bell curve with a sharp spike corresponding to the predominant low background levels within the space. There is another sharp spike at the high intensity corresponding to that of the window and box (Fig. A. 11). There is no internal glare, as there are no two surfaces in high contrast to each other within the room. The high contrast is between the window surface and the background level. The histogram does not show many pixels at intensities between the curve and the high intensity spike, and this accounts for the uneven distribution of intensities across the room. 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^produced D ecem ber 2 1 ,1:00pm, Room 1 22000 20000 18000 16000 » 14000 ................................ - i 12000 ■ — — ................................. 8000 " . 6000 4000 2000 1 ” ......... ii - — w .04 163 172 181 100 100 208 217 226 235 244 253 46 82 100 100 118 127 136 145 154 Intensity Fig. A.11.1 Histogram of Intensity Distribution , * J B | H ■■■ gBBWalw■HH h H B Fig. A. 11.2 Recorded Images Fig. A.11 December 21, 1:00 p.m., Room 1 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. December 21,1:00 p.m., Room 2 The known luminance box is in the 224-256 relative range on the histogram. The upper portion of the window is at the highest luminance of 240 fl. along with the known luminance box and table surfaces. Even with the blinds closed completely there seems to be extremely high background values within the room (Fig. A. 12). The wall behind the monitor is graded in intensity as seen from the histograms (presence of pixels at intensities between the bell curve corresponding to the background and the high luminance of the sky as seen through the window). The contrast between the high intensity and the background is not very high, but it is still a case of corrected glare. This is due to the discomfort caused due to the direct sunlight entering the room. December 21, 2:00 p.m., Room 1 The known luminance box is in the 224-256 range on the distribution. The window and the known luminance box are of the highest intensity of 240 fl. The background levels are low, with a high contrast with the window. However there is no harsh contrast within the room, and this is probably why no discomfort was felt. The histogram show a wide bell curve with a spike at the high intensity corresponding to the window (Fig. A. 13). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. December 21, 1:00pm, Room 2 16000 Fig. A .12.1 Histogram o f Intensity Distribution Intensity _ '< " 1 1 1 1 1 1 1 1 1 I f f 172 181 190 199 208 217 228 235 244 253 m-wwerssaWW Fig. A. 12.2 Recorded Images Fig. A.12 December 21,1:00 p.m., Room 2 109 Reproduced with permission of the copyright owner Further reproduct „ r reProt<Pction prohibited without permission. 22000 Decem ber 21. 2:00pm, Room 1 20000 18000 16000 '/Z ’ .! ;;;; .'.‘ V ,.', ’ .'.f 'r 'i 'i ’ ii’ i '' W 14000 o I , ■ • V 'iiii'i'i'i'i'i'iv 'ri'i'iy I E 3 z 10000 8000 6000 ! ! ' 4000 2000 1 0 0 108 118 127 130 1 4 5 1 5 4 Intensity 163 1 7 9 4 m "-’'iii.iiiiiujiijjjiuim iuflii/niKnrt 163 172 161 100 199 208 217 226 23S 244 2S3 Fig. A. 13.1 Histogram of Intensity Distribution Fig. A. 13 December 21, 2:00 p.m., Room 1 110 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. December 21,2:00 p.m., Room 2 The known luminance box is still at the highest level, setting an absolute range of 0-240 fl. The background levels in the room are pretty high with the upper portion of the window, known luminance box and patches on the work surface being at the highest intensity. The blinds were let down in this image, to cut out the direct light into the room. This is the reason for discomfort rather than the contrast between the high luminance and the background. The wall behind the monitor is also extremely bright, causing the discomfort. The histogram shows a wide bell curve with the hump shifted towards higher background intensities (Fig. A. 14). The peak at the right corresponds to the high intensity areas. Pixels at the intensities between the bell curve and the high intensity correspond to that of the wall surface. December 23,1:00 p.m., Room 1 The known luminance box is in the 224-256 range on the histogram. The predominant background level is low and hence there is a high contrast between it and the window which is at the highest intensity of 240 fl. along with the known luminance box. The histogram shows a wide bell curve, however it is not very smooth. The two big spikes at the hump indicate the dark areas in the image (Fig. A. 15). The spike at the high intensity is that of the window and the luminance box. There is no internal glare since there are no extremely bright or extremely dark surfaces within the room which 111 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with December 21, 2:00pm, Room 2 20000 1 8 000 160 0 0 i E Z 8 0 0 0 6 0 0 0 4 0 0 0 2000 6 4 7 3 8 2 91 1 0 0 1 0 0 1 1 8 1 2 7 1 3 6 1 4 5 1 5 4 1 6 3 1 7 2 181 Intensity W i ^ I ^ w V r u i f f i ' i y a i 'l 190 199 208 217 226 235 2M 2S3 Kg- A. 14.1 Histogram o f Intensity Distribution A. 14.2 Recorded Images Fig. A.14 December 21, 2:00 p.m., Room 2 112 permission of the copyright owner. Further reproduction prohibited without permission. December 2 3 ,1:00pmf Room 1 22000 20000 18000 16000 m 14000 o x ? 12000 10000 6 0 0 0 6000 m iii 1 1 m mu m m »iiiin««iiM » 4000 2000 n w f l W M m M l w h f r w f c ........................................ ....... 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 100 208 217 226 235 244 253 154 163 172 190 190 206 217 226 235 244 253 Intensity Fig. A. 15.1 Histogram of Intensity Distribution Fig. A.15 December 23, 1:00 p.m., Room 1 11 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. could cause discomfort. If the window was part of the field of view of the occupant at that particular instant at his task location, it would have caused discomfort because of its high contrast with the background. December 23, 2:00 p.m., Room 1 The situation is pretty much similar to the 1:00 p.m. distribution. The background levels have gone down lower and the window begins to feel like a source of glare. However there is no internal glare. However the window is at a high contrast with the background. The histogram shows a tall spike at the high intensity corresponding to that of the window (Fig. A. 16). The bell curve is not uniform but wide with a couple of sharp spikes, determining the predominant low background level. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. A-16 D ecem ber 23, 2:00 p .m ., R o o m , 1 1 5 Reproduced with permission of ,he copyright owner. Further reproduce „■ ■ n prohibited without perm ission. APPENDIX B - OCCUPANT SURVEY The following questionnaire was used to survey the occupants while being tested for their response to various contrast situations between the high intensity and background levels within the space OCCUPANT SURVEY SPACE HAR210 DATE TIME WEATHER CONDITIONS CHECK THE FOLLOWING BEFORE STARTING BLINDS down on the rest of the windows DOOR MUST BE CLOSED ---------------------GE meter reading GENERAL SPACE IMPRESSIONS 1. What is the your impression of the space at this particular time? very unpleasant very pleasant o o o o o 116 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Not enough light to work Too much light to work o o o o o Room too dark Room too bright o o o o o Take some time to adjust to each of the three situations before responding to the questions. Setup 1 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? yes no 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? veiy uncomfortable very comfortable o o o o o What is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Setup 2 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? yes no 118 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? very uncomfortable very comfortable o o o o o What is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Setup 3 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? yes no 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? very uncomfortable very comfortable o o o o o What is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Setup 4 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? . yes no 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? very uncomfortable very comfortable o o o o o W hat is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Setup S 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? yes no 121 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? very uncomfortable very comfortable o o o o o W hat is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Setup 6 1. How would you rate the contrast between the window and its surround. Very High Contrast Very Low contrast o o o o o Is there a glare from the window? yes no 122 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. How would you rate the glare from the window? very uncomfortable very comfortable o o o o o W hat is the brightness of the source compared to the brightness of the room? very bright very dark o o o o o Do you have any comments on the quality of light, contrasts or comfort within the space at this time? Thank you for your cooperation. 123 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX C - OBSERVATIONS C-l Observations This is a discussion of the tests and data obtained from the test cell set up at the University of Southern California. Refer Chapter 6 for further analysis and conclusions. March 28, 8:13 a.m. The lights in the room were turned off to lower the background light level in the space. This is seen in the shift of the bell curve towards the left on the histogram, that is towards the lower intensities (Fig. C. 1). The window is at the highest intensity o f340-400 fL, since the known luminance box is in the 160-192 range on the histogram. There is an unequal and ungraded distribution of light intensities across the space as is seen from the gap between the spike and bell curve. There is a high contrast of 5.1 between the window and the background, and is capable of causing extreme discomfort. The occupant responded that there was very high contrast between the window and its surrounds, with the glare from the window being uncomfortable. The window was also very bright in comparison to the rest of the space. March 28, 8:19 a.m. The histogram shows no distinct bell curve, and a very tall spike at the high intensity which corresponds to that of the window. The luminance box is in the 96-160 124 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. range on the histogram which makes the window luminance 370-400 fL (Fig. C.2) The wall surrounding the window adds to the discomfort because of its excessive brightness. The contrast between the high intensity window and background is 3.7. The discomfort is predominantly due to the excessive brightness of the window wall in the field of view of the occupant. The occupant response was that there was glare within the space, which made it uncomfortable, with high contrast between the window and its surrounds. The window was also bright in relation to the rest of the space. March 28, 8:22 a.m. The known luminance box is in the 192-224 range on the histogram. The spike at the right end of the histogram corresponds to the window which is at the highest intensity of 310 fL (Fig. C.3). The wide bell curve indicates a greater spread of intensities across the background. The contrast between the window and background is 3.7, and there willl be slight discomfort felt within the space. The occupant acknowledged the presence of glare from the window which was just bordering on being uncomfortable, with high contrast between the window and the surrounds. The window was not brighter than the rest of the space. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 28, 8:13am aooo 7000 6000 5000 • 4000 ' 3000 • 2 0 0 0 • > * •..................... ......... ,....... , 1 0 0 0 — /-fc -i-r J H t ----------- 0 - ........ I, 11? .ta lf a J k J f J it f t f n H 64 73 82 100 ,0 . 118 * 136 146 ,64 f f g Intensity Fig- C.l.l Histogram of Intensity Distribution Fig. C. 1.2 Recorded Image Fig. C l March 28, 8:13 a.m. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 28, 8:19am I < £ 5 0 0 0 1 10 19 26 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 Intensity Fig. C.2.1 Histogram of Intensity Distribution Fig. C.2.2 Recorded Image Fig. C.2 March 28, 8:19 a.m. 127 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. •ensfry £>/. C O rdedlmi larch 28, 8:22 128 Re~ W hperm /ssfono e C0P yright owner. F u r t „ e March 28, 8:31 a.m. The known luminance box is in the 192-224 range on the histogram. Hence the absolute range of intensities within the space is 0-330 fL. The histogram shows an uneven but still a distinct bell curve. This sets the background level in the space to 68 fL on the relative scale. The spike at the high intensity corresponds to that of the window (Fig. C.4). The contrast between the window and background luminance is 3.9. Because of the higher light levels and grading of intensities across the space, there is not much discomfort felt within the space. The occupant felt that there was glare from the window which was bordering on being uncomfortable. There was high glare from the window with the window being a little brighter than the rest of the space. March 28, 8:32 a.m. There is a shift in the background light level. The background light level is lower and the contrast between the high intensity and background level is high (4.7). The window is in the 192-224 range on the histogram. This establishes an absolute luminance value of 306 fL to the window which is at the highest intensity and is represented by the tall spike at the 255 intensity on the histogram. The bell curve is towards the left of the histogram, with two spikes at intensity 0 and 30 relative (Fig. C.5). This shows that a considerable percentage of the background is at a lower level. There is a large gap between this bell curve distribution and the spike at the end of the histogram. This 129 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. indicates the lack of grading of intensities across the space. There is a high contrast and because of the predominantly low background level, there will be discomfort felt by the occupant. The occupant felt glare from the window which was uncomfortable, with high contrast between the window and the surrounds. However the occupant noted that the extent of the discomfort was reduced because of the presence of the tree near the window, the window was bright in comparison to the brightness of the room. March 28, 8:35 a.m. The histogram shows a wide, flat bell curve, setting a background level of 75 fL relative, that is 106 fL in absolute value. The known luminance box is in the 160-192 range on the histogram (Fig. C.6). From the image it is evident that the window is the source of extreme discomfort, because of the high contrast between the window and the background level in the space. The gap between the bell curve and the spike indicates the lack of distribution of intensities along the wall with the window as well as within the space. This can cause extreme discomfort to the occupant. The adaptation level within the space is 75 fL relative and the contrast between the high intensity and this adaptation level is 3.5. The discomfort is caused due to the high brightness of the window. The occupant felt glare from the window which was excessively uncomfortable, and there was high contrast between the window and its surrounds, and the window was excessively bright in relation to the rest of the surroundings. 130 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F,g. C.4 March 28, 8:31 a.m. 131 Reproduced with permission of (he copyright owner r ■ urther reproduction prohibited without permission. F,g- C s March 28, 8:32 a.m. 132 Reproduced w«h permissiou of the reproduct,ou prohibited without permissiott. 133 Permission o f the b r i g h t owner Fura,„ — e™ ectionn Wout Permission. March 28,8:38 a.m. The known luminance box is in the 160-192 range on the histogram. The bell curve is shifted towards the lower intensities. The contrast between the window which is at the highest intensity and the adaptation level in the space is 4.5. The discomfort felt in this space is because of this high contrast. There is a wide gap between the spike and the bell curve on the histogram indicating lesser distribution of intensities across the space (Fig. C.7). The occupant felt that there was very high contrast between the window and its surrounds, with there being glare from the window which was extremely uncomfortable with the window being excessively bright in relation to the rest of the space. The occupant noted here that he seemed to be getting used to the excessive brightness of the window and the feeling of discomfort was being reduced. March 28, 8:41 a.m. This distribution again shows a bell curve which is wide and spread over a range of 0-122 on the histogram (Fig. C.8). The known luminance box is in the 192-224 range on the histogram, which puts the absolute luminance value of the window to 300 fL. The contrast between the window and the adaptation level is 3.7. The occupant response was that there was low contrast between the window and the surrounds, with no glare from the window. The space was comfortable with the window not being the source of brightness in the field of view of the occupant. As noted earlier there was no discomfort felt by the 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 28, 8:38am s & 5000 II II . T ■ Ltl j . f ll 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 ■kul ilii h a l f M ill i Jl Intensity Fig. C.7.1 Histogram of Intensity Distribution A • ✓ ■ ‘ v.* ' ' ' ^ ' v*s \v.v£ v \ .• .. Fig. C.7.2 Recorded Image Fig. C.7 March 28, 8:38 a.m. 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9000 March 28 , 8:41am 0000 7000 6000 J 2 $ £ 5000 * 5 § 4000 • s 3000 ■ (u iW ,.l| in t,U , || 55 « 73 83 8 , ,0 0 , 0 . „ 8 ,37 ,38 ,4 8 ,54 ,8 3 ,7 3 , 8 , ,9 0 ,8 8 3 0 . 317 ^ Intensity Fig. C.8.1 Histogram o f Intensity Distribution Fig. C.8 March 28, 8:41 a.m. 136 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. occupant within the space, inspite of the high contrast, probably because he was getting adapted to the high intensity of the window. M arch 28, 8:42 a.m. The histogram shows a narrow and taller bell curve which is situated towards the left. The known luminance box is in the 192-224 range on the histogram. The window is still at the highest intensity within the space and hence the glare producing source (Fig. C.9). The absolute value of the luminance of the window is 300 fL approximately. The contrast ratio within the space is 4.8, which is extremely high. This behavior can be traced on the histogram, in establishing the presence of a tall narrow bell curve at one end of the histogram and a tall, high spike at the other end. The occupant did not feel any glare from the window, the space was comfortable and there was low contrast between the window and its surrounds with the window being only slightly brighter than the surroundings. This is an important factor regarding the distribution. If the positions of the spike and the bell curve on the histogram were reversed, it is a case of no glare. This is because the bell curve establishes the predominant background level in the space or the adaptation level, and this case the occupant would be adapted to a higher light level, and the presence of a spike on the histogram would not cause any problem. Another question is how is this spike classified as a glare source or a sparkle? This is where the importance of the video image and color coded images is identified. With a recording of what is in the occupants 137 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith F,S-C .9 March 28, 8:42 a.m. Permission of the copyright owner. field of view and with the color coded image of the space, it can be determined which surfaces are at the highest intensity, and which can be considered as sparkle, or a glare source. Another trend observed was that the height of the spike in relation to the histogram establishes the area or steradians which are at that intensity. In these images, the window has been consistently the source of glare within the room, and occupying an average of 8% of the field of view of the occupant. Of course with a completely controlled test cell where there is no extraneous light within the room, the histogram distribution is cleaned up with a distinct bell curve establishing the background level and the spike representing the high intensity regions. March 28, 8:50 a.m. The histogram distribution is narrow and tall. The bell curve is positioned towards the lower intensities. The known luminance box is in the 192-224 range on the histogram. The absolute range of luminances within the space is 0-300 fL. The contrast between the window which is represented by the spike on the histogram and the background level is 4.8 (Fig. C.10). This contrast is high and causes extreme discomfort. The pixels on the histogram between the bell curve and high intensity peak represent the extraneous light entering the space through the windows located at the side, as seen in the image, the occupant felt there was a very high contrast between the window and its surrounds with Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the glare from the window being very uncomfortable. The window was very bright in comparison with the rest of the space. March 28, 8:56 a.m. The histogram shows a much more uniform distribution of light across the space as seen in the spread of pixels across the entire range of intensities on the histogram (Fig. C.l 1). The known luminance box is in the 160-192 range on the histogram. The range of absolute luminances within the room at this instant were 0-360 fL. The contrast between the high intensity and background is 3.6. The spike at the high end of the histogram is the window, which is at the highest intensity within the space. The occupant felt that there was high contrast between the window and its surrounds, with the glare from the window being uncomfortable. The window was still bright in comparison with the rest of the space. March 28, 9:01 a.m. The bell curve distribution on the histogram is wide and spreads across a greater range of intensities. The window is still at the highest intensity within the space. The absolute range of intensities within the space is 0-360 fL, with the known luminance box in the 160-1792 range on the histogram (Fig. C. 12). The contrast between the window and 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. C.10 March 28, 8:50 a.m. 141 Reproduced w ith permission of the copyright owner Fi.rthP w ' “ ---------------- Py ight owner. Further reproduction prohibited without permission. ensity Distributl 2 ^corded Im. March28,8:56 142 background is 3.7. From the wider bell curve and distribution across the histogram, and the image, it is found that there is not much discomfort felt within the space. The occupant felt only a slight glare from the window and there were no high contrasts within the space. March 28, 9:03 a.m. The histogram shows a narrow bell curve, which is all the way towards the left end of the intensities, that is the lower range. There is a significant gap between the bell curve and the spike which as discussed previously is due to the extraneous light entering the space, as well as the luminance box (Fig. C. 13). The known luminance box is in the 192- 224 range on the histogram. The window is at the highest luminance of 300 fL. There is a high contrast between the window and the background and there is discomfort felt in the space. The occupant felt that there was only a slight discomfort felt by the glare from the window. There is a very low contrast between the window and its surrounds. The occupant did not feel excessive discomfort inspite of the high contrast, probably because of the process of adaptation as discussed earlier. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9000 March 28, 9:01am 8000 7000 6000 • | 5oJ * £ 4000 • 3 z 3000 • 2000 ‘ ' < 1000 • ---------fr- T -|--r. r | { J . 1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 In tensity Fig. C.12.1 Histogram of Intensity Distribution Fig. C.12 March 28, 9:01 a.m. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F'g. C.13 March 28, 9:03 a.m. 145 Reproduced w .h permission of the ^ cfion prohibited without permissiou. March 30, 9:18 a.m. The histogram distribution shows a bell curve which is tall as well as wide. The spike at the right end corresponds to the window. The known luminance box is in the 160-192 range on the histogram (Fig. C. 14). Hence the absolute luminance of the window is 360 fL. The contrast between the window which is at the highest intensity and the background is 4.6. There is some distribution of intensities across the space as seen from the wader bell curve. There would not be excessive discomfort felt within this space, the occupant felt low contrast between the window and the surrounds. There was glare from the window which was uncomfortable, and the window was brighter than the surroundings. M arch 30, 9:21 a.m. The bell curve is wide and there are pixels at almost all intensities within the space (Fig. C.15). The window is still at the highest intensity represented by the spike on the histogram. The known luminance box is in the 192-224 range on the histogram. The window is therefore at a luminance of 300 fL. The contrast between the window and background is 5.7:1. Even though the contrast is very high, the presence of pixels between the curve and the window indicate grading in intensity which reduces the discomfort felt within the space. The occupant felt high contrast between the window and the surroundings, with the glare from the window being uncomfortable. The window was excessively bright in comparison to the rest of the space. 146 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F‘S- C.I4 M arch 30, 9:18 a.m . Reproduced with permission of the common, „ ic copyright owner Fnrfhor reproduction prohibited Fl& C ls March 30, 9:21 a.m. 148 Reproduced with permission of the copyright owner Further reproduce e reproduction prohibited without permission. March 30 9:27 a.m. There is no defined bell curve. There are a couple of spikes at the very low intensities, indicating that a significant portion of the image is at a low intensity (Fig. C.16). The window is still at the highest intensity with an absolute value of 360 fL. The contrast is 4.0 between the glare source and background. The lack of a defined curve is due to excess of unwanted light within the test cell. This dilutes the effect of the bell curve and the position of the spike and its relation to the bell curve. The occupant felt very high contrast between the window and its surrounds. The glare from the window was extremely uncomfortable with the brightness of the window being excessively higher than the rest of the space. The occupant also noted that this was extremely uncomfortable and irritating to the eyes. March 30, 9:31 a.m. The bell curve is again spread across the histogram (Fig. C. 17). The spike at the right end is still the window, although the absolute intensity of the window is now 300 fL. The contrast between high intensity and background is 3.6. Due to the presence of pixels at all intensities, (spread across histogram), the feeling of discomfort in this space is reduced. The spread of pixels across all intensities is also due to the extraneous light within the space. The occupant felt some glare from the window which was bordering on being uncomfortable. There was low contrast between the window and its surrounds and 149 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced ensity E>istributj( K e° o r te d h Z Iarch 30,9:3l 151 R e p r o d u c e d ^ . ,SS,0" W ^ o o p y rte o iv n e r the window was not brighter than the rest of the surroundings. The occupant felt this was distinctly a more comfortable setup than the previous experiment. March 30, 9:34 a.m. The bell curve narrows down considerably with the hump at the lower intensities. The window is still at the high intensity within the space (Fig. C.18). The known luminance box is in the 192-224 range. This makes the luminance of the window to be 300 fL. The pixels between the bell curve spread over the range of 0-110 on the histogram and the spike are due to the excess light entering the cell. The contrast between the window and background is high (4.8) and causes glare. The occupant felt glare from the window which was uncomfortable. The contrast between the window and the surrounds was high. The window was however not brighter than the rest of the space. The occupant observed that he felt this to be the most comfortable of all the setups he was tested in. The contrast ratio within the space was 4.8 and should have caused greater discomfort. It was probably not so because as discussed earlier, this was the sixth setup the occupant was being tested in, and hence he might have become adapted to the high contrast from the window. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 30, 9:34am 9000 8000 7000 .V,! - ! ■ ! , i V'V'jjM 'i'n'i'i'i 6000 t o < u .2S Q . z $ E s Z 5000 4000 * *** * * * —*♦*—— * " 1 1 1 — — ...... Vr "i! 3000 2000 1000 iL..i,.»nA 11» i jrf[j nit ,t4 , n . jitl ri . I 163 172 161 190 199 208 217 226 235 244 253 62 91 100 109 116 127 136 145 154 Intensity Fig. C.I8.1 Histogram of Intensity Distribution Fig. C. 18.2 Recorded Image Fig. C.18 March 30, 9:34 a.m. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 30, 9:39 a.m. The histogram shows a wide distribution of intensities signifying a greater range of light intensities within the space (Fig. C.19). The known luminance box is in the 160-192 range on the histogram, and hence the absolute value of the luminance of the window is 320 fL. The spike in the histogram corresponds to that of the window. There is a contrast ratio o f 3.8 between the window and the background. From the image it is seen that there is a grading of intensities across the window wall, and hence this situation might not necessarily cause extreme discomfort. This behavior is reflected on the histogram in the spread of the bell curve or the presence of pixels at almost all intensities across the space. The occupant response was that there was glare from the window which was bordering on being uncomfortable. The contrast between the window and the surrounds was not high, with the window not being brighter than the surroundings. March 30, 9:41 a.m. The bell curve is shifted towards the left, showing lower background levels (Fig. C.20). The spike at the right corresponds to the window which is at the highest intensity. The known luminance box is in the 160-224 range on the histogram. Therefore the absolute range of intensities within this space is 0-330 fL. There are two distinct spikes at the lower intensity area, showing that a significant portion of the background is at low intensities. The contrast between the window and background is extremely high because 154 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. :nsity Sistributio; -^■K ecordedfo^ 19 March 30, 9:39 155 Permissi0n o f the copyriahf “Pynght ow ner F un h* Reproduced of the lower background levels. This contrast of 5.3 would cause extreme discomfort in the space. The occupant felt high contrast between the window and its surrounds with there being glare from the window, which was slightly uncomfortable. The window was brighter than the rest of the surroundings. March 30, 9:44 a.m. The known luminance box is in the 160-192 range on the histogram, which sets the luminance of the window at 400 fL, which is the highest intensity within the space. The histogram shows a wide spread of pixels across all intensities (Fig. C.21). Correlating it with the image, shows that although a major portion of the image is at very low intensities, it is the extraneous light coming in through the adjacent windows and blinds, that is causing this spread of intensities across the histogram. The window is at the highest intensity again, with is represented by the spike on the right end of the histogram. The contrast between the window and high intensity is 3.7. Although the contrast is not that high, there is extreme discomfort felt within the room, because most of the background is spread across a range of low intensities, and the window along with the wall surrounding it, is extremely bright. The numerical value of the contrast does not reflect this, because as discussed previously, the histogram distribution is effected by the extraneous light entering the space. The bell curve is not a clear distribution from which to determine the background intensity. The occupant felt that there was glare from the window which was 157 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 30, 9:44am 9000 8000 7000 6000 0 9 i £ 5000 ■ 5 •§ 4000 3 z 3000 2000 1000 w a r n l i i n i i A i i f .i.t .j .L i.i .... .f c i i 1 10 19 28 37 46 55 64 73 82 91 100 109 116 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 In tensity Fig. C.21.1 Histogram of Intensity Distribution Fig. C.21 March 30, 9:44 a.m. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. extremely uncomfortable. There was high contrast between the window and the surrounds, although the window was not brighter than the rest of the space. March 30, 9:46 a.m. The known luminance box is in the 160-192 range on the histogram, and the absolute range of intensities within the space is hence 380-400 fL. The spike on the right end of the histogram corresponds to that of the window, since the window is at the highest intensity within the space (Fig. C.22). The bell curve is narrow and positioned towards the low intensity region. There is a high contrast of 4.2 between the window and the background. As seen from the image, most of the background is at the low intensity, it is the window and window wall which are extremely bright and the rest is extraneous light entering through the adjacent windows. This contrast between the window and background would cause extreme discomfort within the space. The occupant felt glare from the window which was extremely uncomfortable. The contrast between the window and the surrounds was high. The window was also brighter than the rest of the space. March 30, 9:50 a.m. The known luminance box is in the 192-224 range on the histogram, which sets the absolute range of luminances within the space to 0-300 fL approximately. The window is 159 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ReProduced still the area of highest intensity and is represented by the number of pixels in the spike at the right end of the histogram. The bell curve is wide and spread across a wider range of intensities (Fig. C.23). This sets the background level to 70fL on the relative range. The contrast between the window and the background is 3.5. The wall with the window is graded in intensity in this case, being at approximately 90-128 fL., and this helps in reducing discomfort by increasing the background level o f the space. There is some glare felt within the space, but the extent of discomfort felt will not be excessive as there is a lower contrast between the window and the background luminance, and grading of intensities within the field of view of the occupant. The occupant felt glare from the window, however there was no discomfort felt. The contrast between the window and the surrounds was very low. The window was equal in brightness to the surroundings. March 30, 9:52 a.m. The known luminance box is in the 192-224 range on the histogram. The absolute luminance of the window is 330 fL since it is at the highest intensity within the space. The bell curve on the histogram is narrow and tall and situated towards the lower range of intensities, which indicates very low background levels (Fig. C.24). This is confirmed by the image which shows that most of the space is at very low luminances, and the contrast between the window and the background is extremely high. The histogram also shows the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. March 30, 9:50am 9000 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 Intensity Fig. C.23.1 Histogram of Intensity Distribution Fig. C.23.2 Recorded Image Fig. C.23 March 30,9:50 a.m. 162 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F,g. C .24 March 30, 9:52 a.m. Reproduced with permission of the copyright owner. Further reproduction Prohibited presence o f pixels in the space between the bell curve and the spike. This corresponds to the luminance of the adjacent windows etc., which is extraneous light within the space. The high contrast ratio of 5 between the high intensity and background and coupled with a lack of grading of intensities along the wall, produces extreme discomfort. The occupant felt glare from the high intensity window, which was uncomfortable. The contrast between the window and the surrounds was however low, and the window was not brighter than the rest of the space. The occupant also noted that he had been in the room prior to the experiment and that he might have already been adapted to the high intensities within the space. This is a significant comment in that it establishes that the issue of adaptation comes up when one occupant is tested continously for varying contrast ratios. April 1,8:42 a.m. The background or adaptation luminance increases again within the space, as seen in the spread and shift of the bell curve on the histogram (Fig. C.25). The window is still at the highest intensity. The known luminance box is also of the highest intensity within the space, which sets the absolute range of intensities within the space to 0-256 fL. The contrast between the window and the rest of the space is 3.2. This change in behavior is noted on the shift in the bell curve and its spread on the histogram. This would not necessarily cause glare. The occupant felt that he could not judge if there was glare or no 164 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 7 4 8 5 5 8 2 9 1 < 0 0 1 0 9 m 1 2 7 1 3 6 1 4 5 1 5 * 1 6 3 1 7 2 1 S 1 1 9 0 1 9 9 2 0 8 2 1 7 2 2 6 2 3 5 intensity Fig. C.25,1 Histogram o f Intensity Distribution '■ « c .2s! 5 S image Fi& C^ A p rilI, 8;42 itn. 165 ,SSI° " 01 'he c°PyVhI o w n e r Fw h glare within the space. There was low contrast between the window and surrounds. The space felt uncomfortable, and the window was brighter than the rest of the surroundings. April 1,8:44 a.m. The beil curve on the histogram is located on the lower intensities (Fig. C.26). The window still remains as the area of highest intensity within the space. The known luminance box is in the range o f224-256 on the histogram. Therefore the absolute luminances within the space are in the range of 0-256. The contrast between the window and background is very high. The bell curve and spike reflect this situation. The bell curve is narrow and tall, and there is a considerable gap between the curve and the spike. This would cause glare. The occupant felt glare from the window which was very uncomfortable. There was high contrast between the window and surrounds and the window was also excessively bright in comparison with the rest of the space. April 1, 8:48 a.m. The bell curve is again wide and spread across a broad range of intensities on the histogram. The spike on the right end still corresponds to the high intensity of the window (Fig. C.27). The known luminance box is in the 224-256 range on the histogram. So the absolute luminance of the window is 256 fL. There is a contrast of 3.2 :1 between the 166 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. C.26 April 1, 8:44 a.m. 167 Reproduced with pemiission of the copyright owner. Further reproducf reproduction prohibited without permission. 9000 April 1 , 8:48am Reproduced with 8000 7000 18 127 136 145 154 163 172 Intensity Fig. C.27.1 Histogram o f Intensity Distribution Fig. C.27.2 Recorded Image Fig. C.27 April 1, 8:48 a.m. permission o f * . copyrigh, „ wnei, Further reproduct|on ^ window and the background and there would not be discomfort felt within the space. The occupant felt no glare within the space, with no harsh contrast between the window and its surrounds. The space was comfortable with the brightness of the window being that of the surroundings. April 1, 8:49 a.m. The histogram shows a bell curve which spreads from 0-100 fL on the relative scale. There is the presence of another distribution between the spike and the bell curve, which reduces the effect of the excessive contrast between the high intensity area and the background. The window is still at the highest intensity, with the luminance box also at 224-256 fL. Therefore the absolute value of the window is 250 fL. The pixels between the curve and the spike correspond to the extraneous light entering the space (Fig. C.28). There will probably be some discomfort felt in this space. The occupant barely felt glare from the window. There was however a high contrast in the luminance of the window and that of the surrounds. The space was uncomfortable with the window being brighter than ther rest of the surroundings. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. F'g. C28 April 1, 8;49 a m Reproduced wilh permission of (he coovrioh, „ eopynght owner. Further reproduction REFERENCES DiLaura, D. L., On the Computation o f Equivalent Sphere Illumination, Journal of the Illuminating Engineering Society, Jan. 1975. DiLaura, D. L., On the Computation o f Visual Comfort Probability, IES Transaction, Journal of the Illuminating Engineering Society, Vol. 5, July 1976, pg. 207. DNNA/Schiler, Marc E., Simulating Daylight-with Architectural Models, DNNA. Egan, David M., Concepts in Architectural Lighting, McGraw-Hill Book Company, 1983. Gillette, Gary, Evaluating Office Lighting Environments, Lighting Design and Application, May 1987, Pg. 4. Gillette, Gary, Collins, Belinda L., Fisher, Will, Marans, Robert W., Second-Level Post-Occupancy Evaluation Analysis, Journal of the Illuminating Engineering Society, Summer 1990, Pg. 21. Guth, S. K., A Method fo r the Evaluation o f Discomfort Glare, Illuminating Engineering, July 1963, Pg. 351. Hopkinson, R. G., Kay, J. D., The Lighting o f Buildings, Frederick A. Prager, England, 1969. Hopkinson, R. G., Evaluation o f Glare, Illuminating Engineering, June 1957, Pg. 305. Hopkinson, R. G., Architectural Physics: Lighting, Her Majesty’s Stationery Office, 1963. Hopkinson, R. G., Petherbridge, P., Longmore, J., Daylighting, Heinemann, London, 1966. IES Subcommittee on Guide for Measurement of Photometric Brightness of the Committee on Testing Procedures of the Illuminating Engineering Society, IES Guide fo r Measurement fo r Photometric Brightness (Luminance), Illuminating Engineering, July 1961, Pg. 457. IES, Lighting Handbook Reference and Application, 8 th Edition, IESNA, New York, 1993. 171 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EES, 1994IESNA Survey o f Illuminance and Luminance Meters, Lighting Design and Application, June 1994. IES, Measurement o f Light and other Radiant Energy, EES Lighting Design Handbook. Kambich, D. G., An Alternative Relative Visual Performance Model, Journal of the Illuminating Engineering Society, Winter 1991, Pg. 19. Lam, William M .C., Sunlighting as Formgiver fo r Architecture, Van Nostrand Reinhold Company, New York, 1986. Lynes, J.A., Principles o f Natural Lighting, Elsevier Publishing Co. Ltd., London, 1968. McGuiness, William J., Stein, Benjamin, Reynolds, John S., Mechanical and Electrical Equipment fo r Buildings, John Wiley and Sons, 8th Edition, 1992. Nawab, Mojtaba, Integration o f Daylighting Design Tools, Lighting Design and Application, March 1991, Pg. 13. Orfield, Steven J., Photometry and Luminance Distribution: Conventional Photometry versus CAPCALC, Lighting Design and Application, January 1990, Pg. 8. Rea, M. S., Pasini Ivaldo, Jutras Louise, Lighting Performance Measured in a Commercial Building, Lighting Design and Application, January 1990, Pg. 22. Rea, M. S., Towards a Model o f Visual Performance: Foundations and Data, Journal of the Illuminating Engineering Society, Summer 1986, Pg. 41. Rea, M. S., Toward a Model o f Visual Performance: A Review o f Methodologies, Journal of the Illuminating Engineering Society, Winter 1987, Pg. 128. Rea, M. S., Jeffrey, I. G., A New Luminance and Image Analysis System fo r Lighting and Vision I. Equipment and Calibration, Journal of the Illuminating Engineering Society, Winter 1990, Pg. 64. Robbins, Claude L., Daylighting Design and Analysis, Van Nostrand Reinhold Company, New York, 1986. Schiler, Marc E., Simplified Design o f Building Lighting, John Wiley & Sons, Inc., 1992. Subcom. on Direct Glare(1972), Preamble by Calculation Procedures Com.(1991), Computing Visual Comfort Ratings fo r Interior Lighting, RQQ Report No.2 with the 1991 Preamble Outline of a Standard Procedure for Computing Visual Comfort Ratings for Interior Lighting, IES LM42, 1991. 172 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Vischer, Jacqueline C., Environmental Ouality in Offices, Van Nostrand Reinhold, New York, 1989. Walsh, John W. T., The Science o f Daylight, Macdonald, London, 1961. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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Asset Metadata
Creator
Japee, Shweta Arun
(author)
Core Title
A method for glare analysis
School
School of Architecture
Degree
Master of Building Science / Master in Biomedical Sciences
Degree Program
Building Science
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
Architecture,OAI-PMH Harvest,physics, optics
Language
English
Contributor
Digitized by ProQuest
(provenance)
Advisor
Schiler, Marc E. (
committee chair
), Noble, Douglas (
committee member
), Schierle, G. Goetz (
committee member
)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c16-2916
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UC11340963
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1379586.pdf (filename),usctheses-c16-2916 (legacy record id)
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1379586.pdf
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2916
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Thesis
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Japee, Shweta Arun
Type
texts
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University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
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Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
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Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
physics, optics