A Lumen Method of Daylighting Design

This paper presents the basis of a new method of daylighting design and daylight prediction for interiors. It has been prompted by the fact that the existing methods of daylight prediction, such as the rectangular surface source methods of Higbie, and Moon and Spenser, the daylight factor or sky factor methods of Waldram and others, and the Fenestra method of Randall and Martin, have been limited in their application by the assumptions made in their development. In general, these methods have been applicable to large spaces such as industrial plants, in which interior reflections and ground reflection have had little significance.

During the past two years, therefore, the major objective of the Daylight Study Project at Southern Methodist University, has been to develop a prediction method which would be applicable to a different range of conditions, to smaller spaces such as classrooms, offices, hospital rooms, small industrial spaces, and the like, in which interior reflections and ground reflections do have significance.

The method outlined in this discussion is based on the premise that it is unnecessary to know the exact illumination at every point in the room, if a determination can be made of the average illumination, the minimum illumination, and the maximum illumination, since these three values would be considered sufficient by the practicing architect and illumination engineer.