AVS 52nd International Symposium
    Science of Semiconductor White Light Topical Conference Monday Sessions
       Session WL-MoA

Paper WL-MoA10
Trapped Whispering-Gallery Optical Modes in White Light-Emitting Diode Lamps with Remote Phosphor

Monday, October 31, 2005, 5:00 pm, Room 310

Session: Science of Semiconductor White Lighting
Presenter: H. Luo, Rensselaer Polytechnic Institute
Authors: H. Luo, Rensselaer Polytechnic Institute
J.K. Kim, Rensselaer Polytechnic Institute
Y.A. Xi, Rensselaer Polytechnic Institute
E.F. Schubert, Rensselaer Polytechnic Institute
J. Cho, Samsung Advanced Institute of Technology, South Korea
C. Sone, Samsung Advanced Institute of Technology, South Korea
Y. Park, Samsung Advanced Institute of Technology, South Korea
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Phosphorescence efficiency in high-power white light-emitting diode (LED) lamps is investigated by three-dimensional ray tracing. It is shown that the absorption of the phosphorescence by the LED chip is greatly reduced by employing a remote phosphor, resulting in the improvement of lamp efficiency. However, for lamps with remote phosphor, a significant fraction of the phosphorescence is found to be trapped as whispering-gallery modes propagating along the circumference of the encapsulant, which causes significant optical loss. The whispering-gallery modes, which occur irrespective of the shape of the encapsulation dome, are shown to be sensitively dependent on the diffusivity of the reflector cup employed in the lamp. Dichromatic LED lamps with remote phosphor were fabricated for reflector cups with different diffusivity. The phosphorescence efficiency is found to be improved by up to 27% for a remote phosphor configuration and a diffuse reflector cup. The experimental results are consistent with theoretical ray tracing simulations.