Verification of the accuracy of the calculated luminance distributions of scaled physical models with directional reflective surfaces

This study verifies the accuracy of the calculated luminance distribution for an actual model with directional reflective surface. The directional reflection properties of materials were modeled using the data measured by gonio-reflectometry and were introduced into a finite element method. After showing the basic calculation formula, we proposed the followings: 1) Subdivision method of facets at corners where the distances between surfaces are short, and 2) the FJIK correction method, which represents the ratio of the luminous flux reflected by facet SI and directly incident on facet SK to the luminous flux emitted from facet SJ and directly incident on facet SI. The applicability of this calculation method to the actual environment was examined by comparing the calculated and measured values for models composed of different inner surfaces whose directional reflection properties had been measured. Results show that the calculation accuracy of the corners were improved for the subdivision method of facets at corners. Moreover, the calculated luminance distribution approached the measured distribution using the FJIK correction method. Furthermore, the luminance distribution differs between the highly diffusive reflection surface and the directional reflective surface even with similar diffuse reflectance, and the maximum luminance of the directional reflective surface changes significantly depending on the viewing angle. We prove that these tendencies can be roughly reproduced using this calculation method. After this research, the accuracy of the simulation considering the directional reflection was improved and it is useful for examining the light environment in detail during the planning stage of a building. •A method for luminance calculation considering directional reflection is presented.•Each reflective surface is divided into triangular facets.•We propose a subdivision and correction method in the calculation.•Experiments using models with glossy surfaces are conducted using a spotlight.•The calculated and measured values are compared via the model experiments.