Traditional computational models predict daylight illuminance in a space by dividing window surfaces into discrete areas and then calculating the apparent luminance of each window element by multiplying the luminance of the natural light source in a given viewing direction by the window transmittance in that direction. This approach works well for conventional glazing materials but is incapable of modeling commonly used, but complex, window systems such, as those with specular reflective venetian blinds. We describe a new approach that combines measured luminance distributions for complex window systems with a flux transfer calculation within the space. This method resembles the calculation of illuminance from electric light fixtures where the candlepower distribution of the fixtures is measured and used as an input to the calculation. Based on the variable luminance characteristics of the window system, the SUPERLITE program calculates illuminance at the workplane over the entire space. The measurement techniques and mathematical implementation in the SUPERLITE program are described. This approach allows a wide range of complex window and shading systems to be evaluated without continuous changes in the computational program. A special apparatus for measuring the bidirectional transmittance of window systems has been built in conjunction with this approach. Sample results from the program are compared to measurements made in scale models in a sky simulator.

%B International Daylighting Conference Proceedings %C Long Beach, CA %8 11/1986 %G eng %L LBL-20542 %1Windows and Daylighting Group

%2 LBL-20542 %0 Journal Article %J Journal of the Illuminating Engineering Society %D 1985 %T Scale Model Measurements for a Daylighting Photometric Data Base %A Mark Spitzglas %A Mojtaba Navvab %A Jong-Jin Kim %A Stephen E. Selkowitz %XWe present initial results of a study to produce a high-precision photometric reference data base using scale model photometry and computational daylighting prediction tools. For this study the SUPERLITE computer code was used. We illustrate the importance and difficulty of fine-tuning the scale model experimental set-up and measurement procedures to produce highly precise results. We discuss the advantage of separating the direct component of illumination from the internal reflected component as an aid to understanding discrepancies between measurements and calculations. We use results of the study to suggest the circumstances in which calculation procedures should be used to generate the references, and those in which the precise scale model photometry is the recommended technique. Further research directions in the field are described.

%B Journal of the Illuminating Engineering Society %V 15 %P 44-61 %G eng %N 1 %1Windows and Daylighting Group

%2 LBL-17286 %& 44 %R 10.1080/00994480.1985.10748633