Coefficients of Utilization for Luminaires with Concentrating Distributions

There is a real need for a method of calculating coefficients of utilization that more fully recognizes differences in distribution of light flux from present day equipment. It would then be possible to provide more accurate coefficients of utilization for use in the familiar Lumen Method formulas.

To satisfy this need the authors are proposing a method of calculating coefficients of utilization that considers the ultimate disposition of the flux from every 10 degree zone instead of using an arbitrary wide zone of 40 degrees as a criterion. The flux in each 10 degree zone that strikes the work plane directly is determined, and to that is added the flux that reaches the work plane by interreflection. The ratio of the total flux reaching the work plane to the lamp lumens is the coefficient of utilization.