Optical elements for mixing colored LEDs to create white light

An experimental study was conducted to investigate the possible use of light guides as mixing elements for mixed color white LED systems. In this study two types of light guides, one with a square cross section and the other with a circular cross section, were systematically analyzed for color mixing. Past literature suggested that square shaped light guides are better color mixers than circular light guides. This study was comprised of two parts: a computer simulation using a commercial ray tracing software package; and an experimental study verifying the results obtained from the simulation. Beam uniformity, in terms of illuminance and color, did not improve significantly with the light guides. System efficiency dropped as a function of length. The measured results matched the simulation results well. Circular and square light guide geometries showed similar performance, contrary to what was suggested in previous literature. Significant improvement of the illuminance and color uniformity was noted when the output ends of the light guides were diffused. This introduced only a small additional loss (6%) in system efficiency.