Effective glass transmission factors under a CIE sky

Abstract

Daylight availability in interiors is reduced because the window glazing is not perfectly transparent. The reduction factor will vary throughout a room according to the angles of incidence of the incoming light on the glazing. This note outlines a new method to calculate the reduction of daylight from a CIE overcast sky due to glazing, which gives accurate results throughout the room. The method is compared with existing methods, and it is shown to be especially appropriate when average daylight factor is calculated by averaging values of daylight factor computed at points on a grid extending throughout the room.