General near‐zone light source model and its application to computer‐automated reflector design

Abstract

The goal of this work is to develop a general light source model that is physically accurate, intuitively descriptive, computationally convenient, and applicable to real sources. It solves two major problems in illumination optics: near zone general extended light source charac- terization for accurate image rendering and ray tracing, and computer- automated reflector design using the resulting near-zone model. The main approach is to combine measurements with Fourier analysis, using judiciously chosen coordinate systems and orthogonal fitting functions. This has several advantages over standard ray tracing: it provides for natural data compression and interpolation; it bypasses the problem of computing the radiance distribution of a real source by using actual pin- hole CCD camera measurements; and it eliminates the computationally intensive ray-filament intersection problem by transforming the source into an equivalent nonuniform spherical radiator. A method for treating the occlusion of rays by the extended filament, with only spherical inter- section calculations, is also discussed. The application of the method is illustrated by the problem of designing a smooth specular reflector to cast a desired intensity distribution on a distant screen for a given source. The problem becomes a straightforward numerical optimization of the perturbations to a base reflector shape. An algorithm to provide a first guess for the perturbations based on the shape of the image perim- eter is also described. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: near-zone light source model; computer-automated reflector de- sign.