Analysis of vertical sky components under various CIE standard general skies

Vertical sky diffuse illuminance data are important for architecture and daylighting designs. In 2003, the International Commission on Illumination (CIE) adopted a range of 15 standard skies representing the actual sky conditions in the world. This paper studies an approach to computing the vertical sky component (VSC) under the 15 CIE Standard Skies. Regression equations for calculating the VSC under various CIE skies based on the scattering angles (χ) were developed to estimate the vertical daylight illuminance on building façades. The performance of the proposed numerical approach and the regression equation are assessed against the results obtained by computer simulations. Our findings show that the VSC data determined by the numerical method and the regression equation are in good agreement with the simulated results. Our research has provided a simple tool for estimating the vertical daylight illuminance under various sky conditions.