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Research Papers

Packaging of Phosphor Based High Power White LEDs: Effects of Phosphor Concentration and Packaging Configuration

[+] Author and Article Information
Yuan-Chang Lin

OptoElectronics Packaging & Materials Lab, University of California, 916 Engineering Tower, Irvine, CA 92697grantycl@gmail.com

Jiun Pyng You

OptoElectronics Packaging & Materials Lab, University of California, 916 Engineering Tower, Irvine, CA 92697jpyou@uci.edu

Nguyen T. Tran

OptoElectronics Packaging & Materials Lab, University of California, 916 Engineering Tower, Irvine, CA 92697ntran3000@yahoo.com

Yongzhi He

OptoElectronics Packaging & Materials Lab, University of California, 916 Engineering Tower, Irvine, CA 92697yzhe2002@hotmail.com

Frank G. Shi1

OptoElectronics Packaging & Materials Lab, University of California, 916 Engineering Tower, Irvine, CA 92697fgshi@uci.edu

1

Corresponding author.

J. Electron. Packag 133(1), 011009 (Mar 10, 2011) (5 pages) doi:10.1115/1.4003216 History: Received November 17, 2009; Revised November 08, 2010; Published March 10, 2011; Online March 10, 2011

Two types of packaged white light emitting diodes in which one has a flat-top (FT) emitting surface and the other is a flat-top-with-lens (FTWL) type are fabricated by using the same leadframe and investigated on their optical properties, such as optical power, luminous efficiency, correlated color temperature (CCT), chromaticity coordinate, and color-rendering index (CRI), as a function of phosphor concentration in silicone encapsulant. It is found out that the optical power, CRI, and CCT decrease steadily as the phosphor ratio increases, while the luminous efficiency increases up to a level and then drops after a certain value of the phosphor ratio for both types of packages. Due to the totally internal reflection (TIR) at the encapsulant-air interface, the FT package shows a 1011% power (in mW) reduction compared with the FTWL package at the same phosphor concentration. However, it is demonstrated that the FT package provides a more efficient way of utilizing phosphor than the FTWL package based on the same targeted chromaticity coordinates due to the TIR effect inside, resulting in a reduced phosphor usage with a lumen output only about 3% lower than that of the FTWL package.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 9

The relative luminous efficiency as a function of CCT (K) for the FT and FTWL packages

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Figure 10

White light emission spectrum for the FT (6 wt % phosphor) and FTWL (8 wt % phosphor) packages

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Figure 8

The CCT (K) as a function of phosphor wt % for the FT and FTWL packages

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Figure 7

Chromatic coordinates (x,y) as a function of phosphor weight percentage in the CIE 1931 diagram together with the Planckian locus curve for the FT and FTWL packages

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Figure 6

The CRI as a function of phosphor wt % for the FT and FTWL packages

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Figure 5

The relative luminous efficiency as a function of phosphor weight percentage for the FT and FTWL packages

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Figure 4

Optical power as a function of phosphor weight percentage for the FT and FTWL packages

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Figure 3

Optical power of high power blue LEDs for three different packaging configurations

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Figure 2

Schematic cross-sectional view of two white LED packages: (a) the FT package and (b) the FTWL package

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Figure 1

Three methods for fabricating white light from LEDs: (a) red+green+blue LEDs, (b) UV LED+RGB phosphors, and (c) blue LED+yellow phosphor

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