RADIANCE DISTRIBUTION ON DENSELY OVERCAST SKIES: COMPARISON WITH CIE LUMINANCE STANDARD

Abstract In this contribution some data measured in Europe are evaluated to enable the comparison of real radiance distributions with the CIE (International Commission on Illumination) luminance gradation approximation of the densely overcast sky. A question is posed whether such a model sky exists in reality, although the frequency of its occurrence might be different in different seasons and in regions with different climates. Eleven cases are evaluated in Figs. 1–3 with the comparison to the cosine and the exponential approximation curves. It seems that the measurement data agree with the CIE Standard but further tests and results obtained during the International Daylight Measurement Programme have to gather more evidence.