The new CIE general sky standard: Daylighting experiences and implications

Markku Norvasuo, Technical Research Centre of Finland, Finland

Keywords

sky model, sky luminance, daylighting, daylight, SSLD, satellight, radiance

Abstract

CIE is currently renewing its sky standards. The new luminance distribution set consists of 15 models, which contain also the current standards. Each sky is defined by five parameters and zenith luminance. The new standard can be applied to many geographic locations and real sky distributions. This is a welcome improvement to the accuracy of modern daylighting tools.

It is already possible to use locally valid daylight data derived from sky measurements. Computer applications such as Radiance and Genelux provide accurate tools for design. However, the problem is how to incorporate SSLD models in both data sources and computational tools.

In the study computational link from the Satellight server to Radiance sky definitions was established. The 13 luminance regions defined by Satellight were converted to the nearest match of the new standard skies. For the implementation, a luminance distribution function was written for Radiance. Even though being provisory, this link makes possible to estimate some implications of the new set.

The models were applied to the sky conditions of South Finland (latitude 60 deg.) in a daylight consultation project. Comparisons between the old and new sets are presented, with reference to the goals of the project. Finally, practical needs are discussed. Since CIE is still preparing the recommendations for the new set, one goal of the paper is to provide a case study for this task.