Spectral ray tracing to model the spectrum of a luminaire equipped with an interference filter

In the lighting community ray tracing is a popular tool for the optical design of luminaires. In most cases it suffices to perform ray tracing at one wavelength, typically 555 nm, because the optical properties of most materials used in luminaire design are not strongly dependent on wavelength. In some special purpose luminaires however, optical components are incorporated to modify the spectrum of the light source. A typical application is the illumination of food products in a retail environment. In this paper it is investigated whether spectral ray tracing can be used to predict the angular variation of the spectrum of a luminaire equipped with an interference filter. The input data for the ray tracing simulations are the experimentally determined spectrum of the light source and spectral scattering properties of the materials in the luminaire, and a geometric model of the luminaire. The spectral radiant intensity of the luminaire at a set of emission angles is measured with a goniospectrometer and compared with the spectral radiant intensity found from the ray tracing simulations. A very good agreement is obtained. Additionally, detailed information is gathered through raytracing simulations, on how the light follows different trajectories through the optical system, contributing to the spectral radiant intensity at different emission angles.status: publishe