The “Reflected Component” in Daylighting Design

Abstract

Present-day methods of designing natural lighting in buildings are still semi-empirical. Usually the light reaching the working plane directly from the sky is the only component considered, whilst all additional light that actually becomes available through reflections and interreflections taking place outside the window and inside the room is neglected. Several attempts have been made in the past, the latest just a few months ago, to develop a more rational approach to the problem. These attempts are reviewed, and it is shown that the first element of the problem, i.e., the determination of the amount of reflected light available in any particular situation, can be solved either on a purely mathematical basis or with the help of suitable model measurements. However, because of the many variables involved, the mathematical solution is necessarily somewhat complicated if it is to yield sufficiently accurate results, whereas experimental investigations tend to deal only with a limited aspect of the whole problem. Moreover, the results obtained by either method will not be of much practical value unless they can be presented in the form of convenient tables or diagrams. Various ingenious suggestions have been made in this respect, but the method recently indicated by Biesele, Arner and Conover appears so far to be the only one which is generally applicable and sufficiently accurate, yet simple and practicable.