Feasibility study of a brute-force ray tracing approach to obtain luminance maps of luminaires modeled with ray files

Abstract

The use of a ray file to model the optical characteristics of a light source is a well-known and popular method to achieve accurate results when simulating luminous intensity distributions of luminaires, especially if the source is interacting with optical components at a close distance. However, lighting industry becomes more and more interested in the spatial luminance distribution of the luminaire itself. Luminance maps offer a tool to predict the degree of discomfort glare early in the design process, especially when developing fixtures using small and intense LED light sources. The generation of luminance maps is commonly based on the reverse ray tracing technique, requiring one or more surfaces to be defined as light sources. However, ray files can not be considered as surface sources, but as a collection of ray data that model the near field of a light source. Despite the fact that ray files are constructed from experimental data they do not explicitly contain the geometry of the light source. This excludes the use of reverse ray tracing. For this reason the implementation of brute force forward ray tracing to obtain luminance maps was investigated. To be able to compare the results of both techniques an inhomogeneous surface source was defined. Luminance maps were then generated using both the brute force ray tracing approach and the conventional reverse ray tracing approach. A good agreement was obtained. A reduction in simulation time was achieved by parallel ray tracing computation and digital enhancement techniques.