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Dip-transfer phosphor coating on designed substrate structure for high angular color uniformity of white light emitting diodes with conventional chips

Huai Zheng, Yiman Wang, Lan Li, Xing Fu, Yong Zou, and Xiaobing Luo

Open Access Open Access

Abstract

Angular color uniformity (ACU) is one of the most important optical parameters of white lighting emitting diodes (LEDs). In this paper, we proposed a kind of phosphor coating method to enhance ACU of phosphor-converted white LEDs with conventional chips by the combination of substrate structure design and phosphor dip-transfer coating. Through this method, compact and optimal phosphor layer arrangements for high ACU can be realized. Optical simulations and experiments were conducted to examine its ACU performance. Compared with conventional phosphor dispensing coating, the present method shows very high ACU performance. Extremely small angular correlated color temperature (CCT) deviations were obtained, which are less than 200K at average CCTs ranging from 4000K to 6000K.

© 2013 Optical Society of America

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Figures (11)
Fig. 1
Fig. 1 Three kinds of phosphor coating structures. (a) Conformal phosphor coating. (b) Conventional phosphor dispensing coating. (c) Designed phosphor structure to enhance ACU.

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Fig. 2
Fig. 2 Schematics of phosphor dip-transfer coating on a cuboid bump structure. (a) Transferring mixture of phosphor and silicone to the end of cylindrical post by dip-transfer coating. (b) and (c) Coating phosphor on top surface of cuboid bump structure. (d) LED module after phosphor dip-transfer coating

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Fig. 3
Fig. 3 Schematic illustration of white LED optical models. (a) LED module with conventional phosphor dispensing coating. (b) LED module with conformal phosphor coating. (c) LED module with present phosphor coating and cuboid bump structure.

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Fig. 4
Fig. 4 Angular CCT distribution comparison between present phosphor coating method, conformal coating and convention coating method at different average CCTs by simulations. (a) About 4500K. (b) About 6000K.

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Fig. 5
Fig. 5 Picture of designed lead-frame LED packaging substrate

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Fig. 6
Fig. 6 Schematic of angular CCT measurement method.

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Fig. 7
Fig. 7 LED modules after completing phosphor dip-transfer coating. (a) Phosphor layer geometry built by Surface Evolver simulation. (b), (c) and (d) Pictures of phosphor layer in top view, angle view and side view, respectively.

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Fig. 8
Fig. 8 Angular color distribution comparison between present phosphor coating and phosphor dispensing coating at average CCT of 4500K.

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Fig. 9
Fig. 9 Angular color distribution of LED modules by present phosphor coating in experiments. (a) CCT distribution at different average CCTs. (b) CCT deviations.

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Fig. 10
Fig. 10 Angular color distribution by optimizing cuboid bump structure. (a) Average CCT of about 4200K. (b) Average CCT of about 6000K.

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Fig. 11
Fig. 11 Luminous efficiency and CRI comparison between present phosphor coating and phosphor dispensing coating at average CCT of 4500K and driving current of 350mA.

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