Etendue conserved color mixing

Abstract

Colored variable lighting is being used in more and more locations to enhance the "beauty" and "atmosphere" of interiors and exteriors. Lamps based on different colored LED are an obvious choice for such systems. The light from the differently colored LEDS needs to be mixed together very well because otherwise objects in the beam could create colored shadows. The difficulty is that we often want a lighting system where the light is collimated, where we can set the color of the beam, and where the lamp is as small as possible with an as small as possible exit diameter. This means that ideally we would like to mix colors etendue preserving. In this paper we discuss a new method of color mixing with dichroic color filters, which aims to achieve this. It is based on a special arrangement of the color filters, whereby the filters act as collimators. We have build prototypes and have done raytracing simulations. These show that we can indeed mix light of different wavelengths and make relatively small, color-variable, collimated, high brightness, light-sources. The advantages are an increase in brightness, a reduction/elimination of the colored shadows, and a small volume. This new method can, e.g., be used in spotlights, mini-beamers and logo projectors.