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Can polarized lighting panels reduce energy consumption and improve visibility in building interiors

Description: The lighting and vision literature, materials on management science and the reflectivity of surfaces are reviewed. The analysis emphasized the connection between lighting design and productivity. It is concluded that polarizing panels should be included among the alternatives normally considered by the lighting designer to utilize energy more efficiently than normal general lighting systems using standard prismatic or diffusing panels. A lighting design using polarizing panels might use 1/4 to 1/3 less energy than a reference system using standard prismatic panels without compromising function. The estimate of the potential energy savings available with polarizing panels is based on the estimate of their efficiency at producing Equivalent Spherical Illumination (ESI). ESI combines the effects of luminance and contrast into a single figure of merit for visibility. A short history and some background of ESI and a discussion of the measured reflectivities of paper and pencil on paper are presented. These data are used in ESI calculations. The problems and limitations of evaluating lighting systems strictly in terms of ESI per watt (or dollar) are discussed. An attempt was made to evaluate polarizing panels in terms of the factors discussed. Additional information is provided in 4 appendices.
Date: August 1, 1979
Creator: Berman, S. & Clear, R.
Partner: UNT Libraries Government Documents Department

Relating productivity to visibility and lighting

Description: The problem of determining the appropriate light levels for visual tasks is a cost-benefit problem. Existing light level recommendations seriously underweight the importance of economic factors. Furthermore, the relative importance of the visibility factors in determining the optimal light levels appears inconsistent with the importance of these factors in determining visibility and visual performance. It is shown that calculations based on acuities give a lower limit of 100 to 200 lux for cost-effective light levels for office tasks. Upper limits are calculated from correlations of task performance to visibility levels. Visibility levels become progressively insensitive to luminance as luminance increases. Average power densities above 100 watts/m/sup 2/ are cost-effective only when visibility is very low. However, there is a 3-to-10 times larger increase in benefits from improving contrast or contrast sensitivity than from using more than 10 watts/m/sup 2/. Contrast or contrast sensitivity can be improved by using forms with larger print, using xerographic copy instead of carbon or mimeo, making sure office workers have the right eyeglasses, or even by transferring workers with visual problems to less visually demanding tasks. Once these changes are made it is no longer cost-effective to use more than 10 watts/m/sup 2/. This conclusion raises serious questions about recommendations that lead to greater than about 10 watts/m/sup 2/ of installed lighting for general office work.
Date: January 1, 1982
Creator: Clear, R. & Berman, S.
Partner: UNT Libraries Government Documents Department

Procedure for calculating interior daylight illumination with a programmable hand calculator

Description: A procedure is described for calculating interior daylight illumination using an inexpensive programmable hand calculator. The proposed procedure calculates illumination at any point within a room utilizing sky luminance distribution functions that are consistent with the CIE (Commission Internationale de l'Eclairage) Overcast and Clear Sky functions. This procedure separates the light reaching the point being considered into three components, these being (a) light directly from the sky, (b) light after being reflected from external, and (c) internal surfaces. Finally, two examples are presented in order to demonstrate the proposed procedure and indicate the speed with which the calculations may be performed.
Date: October 1, 1980
Creator: Bryan, H.J. & Clear, R.D.
Partner: UNT Libraries Government Documents Department

Economics and lighting level recommendations

Description: The Illuminating Engineering Society of North America develops light level recommendations for tasks where visual performance is important. The 1959 and 1972 recommendations for illumination levels were based on the principle of delivering a fixed level of performance as predicted by the visual performance models of the time. This same principle is being considered for future revisions to the recommendations. There is currently no explicit method for determining whether a given fixed performance level is in any sense optimal or best. Visual performance increases with lighting levels, but so do economic and environmental costs. These costs lessen the economic benefits of the improved visual performance. A formal method for including these factors in light level recommendations is to restate the problem in terms of net benefits (benefits minus costs). The resulting equations have well defined optima versus light level, and thus give an explicit estimate of what the best lighting levels are in terms of current visual performance models, and current economic conditions. A simple net-benefit procedure is described, and sample calculations are shown for two current visual performance models. Fixed performance levels do not provide economically optimal recommendations with either model. There are also differences between models, but they are less significant than the large differences between the principles of fixed performance levels and economic optimization.
Date: April 1, 1992
Creator: Clear, R. & Berman, S.
Partner: UNT Libraries Government Documents Department

Size as a determinant of reading speed

Description: The speed of reading unrelated words as a function of luminance, size, and contrast, was measured with an eye movement monitor for fifteen young adults. Subjects read up to 5,000 words in a test session, with the exact number depending upon their acuity. The size of the smallest legible print at a given luminance and contrast for these subjects was found to fit well to the Blackwell-Taylor detection threshold data above about 1 minute of arc. At lower sizes inclusion of a resolution size term provided an excellent fit. Reading speed was fit to a number of visual performance models. It was found that for most subjects that a ratio of the print size to an estimate of the threshold print size (a VL[sub size]) gave the best fits to the data. The threshold size was computed with a fit to the Blackwell-Taylor detection threshold data, modified to include a resolution size term as above. For the sole remaining subject a slightly better fit was obtained with a VL[sub contrast] model, where again the thresholds were modified by a limiting size term. The implication of these results for visual performance modeling is discussed. The reading speed for all subjects varied rapidly with size near the acuity limit, but became almost independent of visibility parameters as long as size is two times the acuity limit. These results show that size is a powerful determinant of reading speed, and suggest that minification of about 1/2 power could be used as a field test for adequate visibility.
Date: March 1, 1992
Creator: Bailey, I.; Clear, R. & Berman, S.
Partner: UNT Libraries Government Documents Department

Size as a determinant of reading speed

Description: The speed of reading unrelated words as a function of luminance, size, and contrast, was measured with an eye movement monitor for fifteen young adults. Subjects read up to 5,000 words in a test session, with the exact number depending upon their acuity. The size of the smallest legible print at a given luminance and contrast for these subjects was found to fit well to the Blackwell-Taylor detection threshold data above about 1 minute of arc. At lower sizes inclusion of a resolution size term provided an excellent fit. Reading speed was fit to a number of visual performance models. It was found that for most subjects that a ratio of the print size to an estimate of the threshold print size (a VL{sub size}) gave the best fits to the data. The threshold size was computed with a fit to the Blackwell-Taylor detection threshold data, modified to include a resolution size term as above. For the sole remaining subject a slightly better fit was obtained with a VL{sub contrast} model, where again the thresholds were modified by a limiting size term. The implication of these results for visual performance modeling is discussed. The reading speed for all subjects varied rapidly with size near the acuity limit, but became almost independent of visibility parameters as long as size is two times the acuity limit. These results show that size is a powerful determinant of reading speed, and suggest that minification of about 1/2 power could be used as a field test for adequate visibility.
Date: March 1, 1992
Creator: Bailey, I.; Clear, R. & Berman, S.
Partner: UNT Libraries Government Documents Department

Office worker response to an automated venetian blind and electric lighting system: A pilot study

Description: A prototype integrated, dynamic building envelope and lighting system designed to optimize daylight admission and solar heat gain rejection on a real-time basis in a commercial office building is evaluated. Office worker response to the system and occupant-based modifications to the control system are investigated to determine if the design and operation of the prototype system can be improved. Key findings from the study are: (1) the prototype integrated envelope and lighting system is ready for field testing, (2) most office workers (N=14) were satisfied with the system, and (3) there were few complaints. Additional studies are needed to explain how illuminance distribution, lighting quality, and room design can affect workplans illuminance preferences.
Date: March 1998
Creator: Vine, E.; Lee, E.; Clear, R.; DiBartolomeo, D. & Selkowitz, S.
Partner: UNT Libraries Government Documents Department