CIE standard sky model with reduced number of scaling parameters

摘要

The calculation of diffuse horizonthal illuminance D _v outdoors is generalized and interrelated to parameters that characterize the sky luminance distribution function. The derived analytical formula for D_(V.rel) which is D_v normalized using luminance in the zenith can be commonly applicable to all 15 ISO-standardized sky types. This makes the modelling of all 15 skies more uniform than ever before. The presented analytical solution is simplified enough because the set of 60 parameters B_1, C_1,D_1,E_(1)- B_(15), C_(15), D_(15), E_(15) scaling the diffuse illuminance is no more necessary in the new solution. In addition, the analytical formulae substituting the empirical ones are valid for all solar altitudes r γ_s (including the situations with sun in zenith). On the contrary, the empirical formulae may become inapplicable for γ_s > 75° and fail whenr γ_s approaches 90°. Compared with detail numerical integration the analytical formula guarantees more rapid calculation of Dvre/.