PREDICTING SOLUTIONS TOWARDS IMPROVED HIGH POWER WHITE LED LIGHT SOURCES - A COMBINED THEORETICAL AND EXPERIMENTAL STUDY

摘要

To compete with and to surpass the performance of traditional lighting systems, white LED development is still facing the necessity of further improvements. An important topic that has to be addressed in this context is the spatial homogeneity of the white light emitted, an issue that is directly associated with the geometry and the composition of the color conversion elements (CCE) in phosphor converted LEDs. In order to avoid the need for experimental realization and inspection of a large number of different configurations and compositions, optical simulation provides a time- and cost saving alternative. In this contribution we discuss a simulation procedure which allows us to predict optimized solutions for the CCEs in white LED light sources. The simulation process involves the set-up of a model for the blue emitting LED chip and the implementation of a multitude of different geometries and compositions of individual CCEs on top of the chip. Since the light is scattered within the CCEs, the respective scattering model, which considers the phosphor particle size distribution and the phosphor weight fraction is of particular importance. In the final sequence of the modeling procedure color uniformity is checked by monitoring the irradiance distributions both for the blue LED light and the yellow converted light separately on a detector. From a comparison of the simulation results for a significant number of different layouts we can deduce the impact of the individual materials parameters and predict optimized CCEs which are finally compared with real device set-ups in order to verify the accuracy of the simulation procedure.