Determination of Total External Illuminance on a Sloped Surface from Sunlight and Skylight

Easy to use tables of external illuminance values for sloped surfaces can contribute to the ease of the design for buildings that contain skylights in a pitched roof. The number of skylights, area of the skylights, orientation of the skylights, etc. are more easily determined for the predetermined level of illumination required when the external illuminance on the skylights' surface is known. Equations such as the Moon-Spencer equation (overcast sky luminance distribution) and the Kittler equation (clear sky luminance distribution) are utilized in developing mathematical models for determining the exterior illuminance values.