Studies on Optical Consistency of White LEDs Affected by Phosphor Thickness and Concentration Using Optical Simulation

Effects of variations of yttrium aluminum garnet:Ce phosphor thickness and concentration on optical consistency of produced white light-emitting diodes (LEDs) including the consistency of brightness and light colors were studied by optical simulation. Five packaging methods with different phosphor locations were compared. Optical models of LED chip and the phosphor were presented and a Monte Carlo ray-tracing simulation procedure was developed. Both color binning and brightness level were used to sort the simulated LEDs to evaluate their optical consistency. Results revealed that the optical consistency of white LEDs strongly depends on how the phosphor thickness and the concentration vary. To obtain desired color binning, conformal phosphor coating is not a favorable packaging method due to its low brightness level and poor brightness consistency by large shifts of the brightness level as the phosphor thickness and concentration varying. Planar remoter phosphor improves the brightness level and its consistency, but realization of high color consistency becomes more difficult due to its smaller variation ranges of the phosphor thickness and concentration. Hemispherical remoter phosphor can fulfill the requirements of both high color consistency and high brightness consistency due to its capability of larger variation ranges of the phosphor thickness and concentration. By applying this method with thick phosphor thickness or high phosphor concentration, this method can be a promising packaging method for the low cost production.