The Spectral Power Distribution of Daylight

The factors controlling the spectral distribution of power of daylight at ground level are described and their effects are discussed. A résumé is given of recent experimental studies of the subject. The author's recent work is described in outline: a large number of measurements have been made in higher resolution than previous studies, and measurements have also been made in London and the country to investigate the effect of atmospheric pollution. Attempts were made to correlate the results with the prevailing sky conditions. The results of all the recent studies are compared, and over the visible range they are in reasonable agreement: this is not the case in the near ultra-violet range. Conclusions are put forward which it is hoped will be of value to the lighting engineer and architect.