Analysing sky luminance scans to obtain frequency distributions of CIE Standard General Skies

Abstract

The CIE Standard General Sky consists of a family of luminance distributions which can be matched to measured sky brightness patterns. The daylight climate of a site can be described concisely and effectively by the statistical distribution of the General Sky types that best fit the sky luminance patterns that occur there. This paper gives a procedure for deriving the frequency of occurrence of General Sky types from International Daylight Measurement Programme sky scan data. Measured luminances are normalized with respect to horizontal illuminance and solar elevation, then the sky types giving the best least-squares fit are found. A data structure for daylight climate simulation is proposed.