Recently various lighting designs have become required more than ever. In order to closely examine and appropriately design various light environments, highly accurate luminance predictive simulation techniques are needed. Since luminance distributions are influenced more by directional reflection characteristics than by illuminance distributions, it is necessary to obtain data of directional reflection characteristics for luminance simulations. In this study, in order to easily obtain data of directional reflection characteristics to be incorporated into the simulation, we considered to identify feature quantity of mathematical models of directional reflection characteristics by using information obtained by employing simplified measurements. As the simplified measurements method, we attempted to utilize the physical properties of building materials which have recently been made easily measurable by using commercially available instruments. From the attempts in this study, the followings were found.
(1) We compared detailed data set of directional reflection characteristics, which were obtained by the direct measurement method utilizing polarizers, with such physical properties as glossiness and surface roughness Ra measured by using commercial measuring instruments. From these, it was found that the larger the glossiness and the smaller the surface roughness Ra, the larger the boundary reflection component tended to be and the sharper the distribution characteristics of the boundary reflection component tended to be. However, other than the correlation between the glossiness and the intensities of the boundary reflection component were low.
(2) We compared the detailed data set of directional reflection characteristics with spectral diffuse reflectance measured with commercially available instruments. It was found that there was a strong correlation between the layer reflectance RD and the diffuse reflectance under the light source used for the measurement, which were calculated from spectral diffuse reflectance (SCE).
(3) We proposed a method to model directional reflection characteristics based on simplified measurements without polarizers, which gives the estimation of layer reflection characteristics derived from the diffuse reflectance. In this method, the number of measurement steps was capable of being reduced to one-fifth, and the same accuracy as detailed measurements with polarizers was able to be obtained. The method was verified for surfaces with semi-uniform diffuse reflection characteristics and not verified for surfaces with specular reflection characteristics.
(4) The directional reflection characteristics of the five building materials with different finishes, such as a polished marble tile, highly polished marble tile, a fair-faced concrete block, a semi-gloss galvanized steel plate and float glass, were successfully obtained by the simplified prediction method.
(5) For building materials with high glossiness, it is considered necessary to measure them by setting the measurement incident angle conditions at least three times in order to determine with sufficient accuracy the coefficient K which is the feature quantity of the layer reflection component.
