An Approximate Calculation of Interreflections in Rooms with Mixed Diffuse-Specular Surfaces (Part 2)

Abstract

Illuminance and luminance distributions in rooms are strongly influenced by the reflectance characteristics of the surfaces.
The goniophotometric properties of many practical surfaces can be considered as exhibit both a diffuse and a specular component of reflectance.
The reflectance of the mixed diffuse-specular surface is apparently influence by the angle of incidence of the light.
This paper describes an approximate calculation method of interreflections it rooms with the mixed diffuse-specular surfaces considering the effect of the angle of incidence of the light.
The approximation is based on the assumption that mixed diffuse-specular surfaces can be treated solely as uniform diffusers for all interreflections.
Calculated values of the luminous exitance of the floor surface by this method are compared with mesured values and showed the effect of specular and diffuse wall reflectance components on the average illuminance of the floor surface is shown.
The results show that significant errors occur if the reflectance of the mixed diffuse-specular surfaces is treated to be unaffected by the angle of incidence of the light.