A computer model for lighting prediction

Abstract A previous article[1] by one of the authors demonstrated the important role played by brightness patterns and distribution in the description of what is loosely termed the ‘character’ of an interior, its spaciousness, warmth and restfulness. This paper describes a computer programme developed by the authors, to predict luminance and illuminance levels in any rectilinear environment with considerable accuracy. Sources of light may be both natural—sun, sky and grounf surface—and artificial, as point, linear and area fittings, each BZ-classified. The program simulates inter-reflection by dividing each surface into numerous “cells” and considering the exchange of ligth between all pairs of cells. Results can be made as accurate as desired, at the expense of increased computation time; the authors have carried out a photometric experiment the results of which were found to correlate to within 15% with values obtained from the equivalent computer simulation. Much time and manpower spent on objective scale model studies can now be largely eliminated by this means. This program should prove a highly useful predictive tool due to its versatility and the number of possible options it contains. More complex building configurations can be analysed, such as courtyard conditions or rooms which are non-rectangular or contain partitions and furniture. Illuminance can be predicted at any set of positions as planar, scalar or vector values.