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Abstract
The amount of daylight illuminance at a point inside a building is mainly influenced by the luminance levels and patterns of the sky in the direction of views of the surface at that time. The daylight coefficient approach, which considers changes in the luminance of the sky elements, offers a more effective way for computing indoor daylight illuminances. Recently, Kittler et al. have proposed a new range of 15 standard skies including the CIE (Commission Internationale de l'Eclairage) standard clear sky. This paper presents a graphical method to calculate interior illuminance for the CIE standard clear sky based on daylight coefficient concept. The simplified techniques in the form of a nomograph and Waldram diagram were developed and described. The performance of the graphical method was assessed against the results determined using daylight factor method and a lighting simulation program. It was shown that the sky components predicted by the nomograph were in reasonably good agreement with those produced from the other two approaches. The findings provide architects and building designers a reliable and simple alternative that incorporates daylight coefficient concept to estimate the interior daylight illuminance.