LBNL Report Number
An analytical model and a computer code have been developed which calculate the amount of daylight illumination on a working surface inside an arbitrary room, for overcast as well as for clear sky conditions. The room may have windows as well as skylights, with clear glass, diffusing glass, or glass fitted with thin shading devices (such as sheer curtains or shades), as well as overhangs. The shape of the room is not limited to simple, rectangular enclosures, allowing the treatment of L-shaped rooms, A -frame buildings, etc.
The illumination generally consists of three parts: direct sky illumination, illumination from external reflection, and illumination from internal reflection. First, the luminances eminating from surrounding obstructions are determined. Next, illumination traveling through the windows directly to inside walls and working surface is calculated. Finally, interreflection inside the room is taken into account to establish the luminance distributions of inside walls. After determination of all inside and outside luminances, it is a simple matter to calculate illumination and daylight factor for the working surface.