There are several methods available to determine the coefficient of utilization which is an important factor for predicting illumination levels of an interior lighting installation. As well known, Harrison-Anderson Method, the Zonal Cavity Method, the British Zonal Method, the CIE Method and so on have been used selectively in various countries.
The authors highly appraise the CIE Method among them, because of its theoretical exactness and practical simplicty. However, it had some points left to be improved, particularly the convenience for mechanical computation. They developed an improved method fit for complete computerization, which is called the CIET Method.
In the course of its applications, they surveyed the effect of the implantation of lighting fittngs in order to prepare practical tables of coefficients of utilization, and also to apply the curveplotter for drawing the isolux curves, taking into account both the direct illuminance and the diffused illuminance due to interreflection.
As the result, two computer programs, i. e. one for preparing practical tables of coefficients of utilization and the other for plotting isolux curves in any given condition, were developed.