Characterization of sky scanner measurements based on CIE and ISO standard CIE S 011/2003

The aim of this paper is to present a complete analysis of the sky luminance distribution data measured with a sky scanner at the International Daylight Measurement Program station in Lyon. Besides presentation of the sky luminance distribution, we also derive the CIE sky type based on the CIE S 011/2003 standard. The CIE sky type is based on gradation and indicatrix functions. Determination of the gradation and indicatrix group is based on the calculation of luminance ratio between two elements on every almucantar. Since there are six gradation and six indicatrix groups, we have 36 combinations but only 15 of them are listed in the CIE standard. Since some of combinations are really rare, we provide a table to show how to allocate 36 combinations to 15 standard CIE sky types. At the end of the paper, we present frequencies of occurrence of CIE sky types in Lyon.