Simulating and calculating sky luminance distribution with CIE standard DS 011.2

Abstract

For over half a century, the experts have been trying to describe the daylight and sky luminance distribution with different models. Different approaches were used to describe the luminance of sky in different weather and climactic conditions. But until recently, only two types of sky had been standardized: The CIE Standard Clear Sky and Overcast Sky. As the use of daylight is gaining on importance in the lighting design, the TC 3 at CIE also started drafting a standard description of other types of sky between clear and overcast sky. The new standard will be used in calculations of lighting conditions in interiors lit by natural daylight. In the paper, the new CIE standard is described together with two computer programs developed in our laboratory. The first program is used for calculation of the position of the Sun according to the point of observation on the Earth and time (date). The position of the Sun is then used in the second program for calculation of the sky luminance distribution according to the proposed standard. The program calculates the luminance of 77 patches representing the sky vault. The luminance of this sky model will then be used for calculating lighting conditions in interiors lit by daylight.