18 August 2010 The effects of titania diffuser on angular color homogeneity in the phosphor conformal coated white LEDs
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Abstract
White light-emitting diodes (LEDs) have dramatically developed and gradually taken over from the conventional light source as the solid-state lighting during the last decade. It is now sufficient for illumination application in performance, while it is still insufficient in color quality. Especially, most of phosphor-converted white LEDs have the poor angular color homogeneity. In this study, we adopted a distinctive phosphor conformal coating technique in the packaging process to reduce the variance of correlated color temperature (CCT) among the packages and spatial CCT in the package. Also, to reduce the spatial CCT variance without considerable shrinkage of luminous efficacy, we applied submicrometer scale TiO2 powder as diffuser in the phosphor layer or in the encapsulation layer of white LED with a phosphor conformal coating layer and investigated the effects of titania diffuser on angular color homogeneity and optical performance. Regardless of the diffuser content, spatial CCT variance and luminous efficacy were decreased with the increase of the diffuser content. Nevertheless, among the conditions for achievement of the equivalent in color uniformity, the luminous efficacy in the case of 0.1 wt% diffuser mingled in the encapsulation layer was 20 % higher than in the case of 5 wt% diffuser mingled in the phosphor layer. These phenomena result from differences of light scattering loss caused by 10 times more volume of diffuser mixed in the phosphor layer than in the encapsulation layer.
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Kwang-Cheol Lee, Sang-Mook Kim, Jong-Ha Moon, "The effects of titania diffuser on angular color homogeneity in the phosphor conformal coated white LEDs", Proc. SPIE 7784, Tenth International Conference on Solid State Lighting, 778410 (18 August 2010); doi: 10.1117/12.861108; https://doi.org/10.1117/12.861108
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