Sawtooth rooflights : Efficiency at different sky states

Abstract

The lighting efficiency of sawtooth rooflights for clear sky and overcast sky conditions is evaluated by computer using the finite luminous element method. The daylight factor components for the direct sky lighting of the work plane and the inclined rooflight ceiling, reflected light on the plane and the light reflected from the adjacent roof and falling into the sawtooth rooflights are discriminated. The procedure takes into account the effect of direct sunlight on the formation of the luminous environment in a room. Empirical formulae suitable for fairly straightforward computations of these components are presented. Consideration of direct sunlight by this approach provides for a 25% reduction of the glazing area or an increase in the period during which daylight can be used in a room, and thereby a considerable lighting energy saving.