All Sky Model as a Standard Sky Luminance Distribution — Part 2 A Numerical Expression of Sky Luminance Distributions for All Sky Conditions —

The aim of this research work is to establish a standard sky model for designing excellent daylighting schemes that cover all sky conditions from clear sky to overcast sky. In the previous paper (Part 1) 1), the “normalized global illuminance” was defined as a function of the measured global illuminance and the solar altitude for estimating the sky luminance distribution. In this paper (Part 2), the “Relative All Sky Model” is introduced. It offers formulas to show the relative sky luminance distribution as a function of the normalized global illuminance. The equation of the zenith luminance concerning the Relative All Sky Model is also a function of the normalized global illuminance. It is called the “All Sky Zenith Luminance” An absolute standard sky luminance distribution model called the “All Sky Model” is introduced that is a multiplication of the Relative All Sky Model and the All Sky Zenith Luminance. The All Sky Model can be calculated from the normalized global illuminance, i.e., from the measured global illuminance and the solar altitude or from the measured global illuminance, the horizontal diffuse illuminance, and the solar altitude. The global illuminance and horizontal diffuse illuminance are easily obtained from even the simplest daylight measurements.The All Sky Model can produce an excellent standard sky for daylighting design for any place where an advanced daylight environment is needed. KEYWORDS: sky luminance distribution, standard sky, daylighting design, All Sky Model.