Luminance distribution characteristics of homogeneous skies: a measurement and prediction strategy

Abstract

In the context of energy conservation the time-averaged and unsteady characteristics of the daylight climate are significant. The intermediate sky luminance patterns of the homogeneous turbid atmospheres form a gradual transition between the CIE 'Clear' and 'Overcast' skies. These patterns are influenced by the scattering of sunlight due to the turbidity of the atmospheric layers as defined by the diffusion indicatrix, while at the same time changes in the vertical sky luminance graduation take place. Contrary to overall scanning luminance measurements this paper suggests methods to identify the indicatrix and gradation characteristics by specific trace circle measurements on the sky vault, and proposes provisional relations expressing their dependence on the illumination turbidity factor of the atmosphere.