Simulation and experimental studies of phosphor concentration and thickness for phosphor-based white light-emitting-diodes

The dependence of luminous efficacy on phosphor concentration and thickness for high-power white light-emitting-diode (WLED) lamps is investigated by employing three-dimensional ray-tracing simulations. The simulations show that the brightness or luminous efficacy of WLED lamps highly depends on the combination of phosphor concentration and phosphor thickness (or phosphor-matrix composite volume). The package with lower concentration and higher phosphor thickness has higher luminous efficacy because the light trapping efficiency is lower with the low phosphor concentration. Our simulations demonstrating a 20% and 27% improvement in lumen output with 1.8mm-phosphor package over 0.8mm-phosphor package and 0.6mm-phosphor package respectively are found to be fully supported by experimental observations.