Technical Papers and Presentations

High-powered solid-state lighting uses ceramic materials for conversion of impinging blue pump light into bright longer-wavelength luminescence. This luminescence combines with an unconverted portion of the blue pump light to provide a white light spectrum. As the conversion efficiency degrades with temperature, the heat generated in the conversion process increases temperature, leading to a degradation of the light output. To anticipate thermal limits of operation, we model the optical processes, the thermal process, and the two-way coupling between them. The method applies only to cases in which scattering is high inside the converter, enabling the radiation transfer to be modeled as a diffusion process. We show how the diffusion approximation is formulated, where the thermal coupling occurs, and describe how full model fits well in the PDE models implemented in COMSOL Multiphysics^® simulation software. A simple example is presented to show how the model predicts light output together with its dependence on the thermal runaway condition that ultimately limits light output at the highest blue pump light intensities.