Analysis of high-power packages for white-light-emitting diode lamps with remote phosphor
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Analysis of high-power packages for white-light-emitting diode lamps with remote phosphor Hong Luo1, Jong Kyu Kim2, Yangang Xi1, E. Fred Schubert1,2, Jaehee Cho3, Cheolsoo Sone3, and Yongjo Park3 1 Department of Physics, Applied Physics and Astronomy 2 Electrical, Computer, and Systems Engineering Department Rensselaer Polytechnic Institute, Troy, New York 12180 3 Photonics Program Team, Samsung Advanced Institute of Technology, Suwon 440-600, South Korea ABSTRACT An optimized packaging configuration for high-power white-light-emitting diode (LED) lamps that employs a diffuse reflector cup, a remote phosphor and a hemi-spherically-shaped encapsulation is presented. Ray tracing simulations for this configuration show that the phosphor efficiency can be enhanced by up to 50% over conventional packages. It is experimentally shown that dichromatic LED lamps with remote phosphor and diffuse reflector cup configuration have higher phosphor efficiency by 15.4% for blue-pumped yellow phosphor and by 27% for ultraviolet-pumped blue phosphor over conventional packages. Those improvements are attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant. INTRODUCTION With the rapid development of high-power white-light-emitting diodes (LEDs) and its potential for general illumination applications, there is a need for new high-power packaging technologies with low thermal resistance, compact size and high efficiency [1]. The combination of a phosphor wavelength converter with a short-wavelength primary emitter is a common method for LED-based white light sources. For example, a GaInN blue LEDs pumping a yellow YAG:Ce phosphor can generate dichromatic white light by mixing the two complementary colors. High photon out-coupling efficiency is particularly important for high-power LED lamps. The reflector cup, the placement of the phosphor, and the geometry of the encapsulation dome strongly influence the efficiency of the lamps. In common configurations, the phosphor is either distributed uniformly in the reflector cup [2] or located in a layer replicating the contour of the LED chip (proximate conformal phosphor distribution) [3] as shown in Figure 1 (a) and (b). These “proximate phosphor” arrangements limit the phosphor efficiency because a portion of light generated by the phosphor is emitted towards the absorptive LED chip. Separating the phosphor from the LED chip by a large distance [4, 5], which is referred to as “remote phosphor” as shown in Figure 1(c), reduces the probability of the phosphorescence being absorbed by the chip and thus improves the phosphor efficiency. For improving the extraction of light emitted by the LED chip and the phosphor out of the lamp package, encapsulations with different geometries have been employed. However, trapped optical modes inside the lamp package can occur, especially for high-power LED packages with compact size and relatively small encapsulant domes. Diffuse reflector cups can h
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