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Proceedings Paper

Improving the performance of mixed-color white LED systems by using scattered photon extraction technique
Author(s): Huiying Wu; Nadarajah Narendran; Yimin Gu; Andrew Bierman
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Paper Abstract

One of the methods for creating white light with light-emitting diodes (LEDs) is mixing radiations from several different colored LEDs. Mixed-color LEDs are expected to have greater luminous efficacy because they do not undergo down-conversion losses like phosphor-converted white LEDs. However, in reality mixed-color LED systems require extra optical elements to reduce spatial color variation and create uniform white light. Optical diffusing techniques commonly used for these purposes cause light loss, because some portion of the light is scattered back toward the LEDs where it is absorbed and lost. In 2004, a technique known as scattered photon extraction (SPE) was used to extract backscattered light from the phosphor layer of phosphor-converted white LEDs to increase overall light output. In this study, it was hypothesized that by using similar SPE optics with optical diffusers, the spatial color uniformity of mixed-color white LED systems could be improved without sacrificing the overall luminous efficiency. With this new approach, both a microsphere-doped diffuser and SPE optics were utilized. The experiments showed that the proposed setup did increase the spatial color uniformity of the mixed-color LED system with more than 79% overall optical efficiency. This study also demonstrated the effects of microsphere size, concentration, and diffuser thickness on spatial color uniformity and optical efficiency.

Paper Details

Date Published: 17 September 2007
PDF: 12 pages
Proc. SPIE 6669, Seventh International Conference on Solid State Lighting, 666905 (17 September 2007); doi: 10.1117/12.746777
Show Author Affiliations
Huiying Wu, Rensselaer Polytechnic Institute (United States)
Nadarajah Narendran, Rensselaer Polytechnic Institute (United States)
Yimin Gu, Rensselaer Polytechnic Institute (United States)
Andrew Bierman, Rensselaer Polytechnic Institute (United States)

Published in SPIE Proceedings Vol. 6669:
Seventh International Conference on Solid State Lighting
Ian T. Ferguson; Nadarajah Narendran; Tsunemasa Taguchi; Ian E. Ashdown, Editor(s)

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