Efficiency analysis and prediction method of phosphor-converted LED with blue-pumped remote phosphor structure
Hwang Jung Min1*, Mei-Tan Wang1
1Advanced Lighting Technology Department, Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsin-chu, Taiwan
* presenting author:HWANG JUNG MIN, email:jmhwang@itri.org.tw
Light-emitting diodes (LEDs) become a major lighting source in 21st century due to its high efficiency and high reliability. Using blue LEDs to pump yellow phosphor is still the mainstream way to produce white light LED. The blue pumping light is absorbed by phosphor then converted into longer wavelength with board full width at half maximum (FWHM). The structure of remote phosphor is proposed to reduce the phosphor thermal decay. Through changing the blue light absorption ratio of phosphor will be able to adjust the efficiency and color of the light source. In this study, the distance between blue LEDs and single yellow phosphor plate was changed from 20mm to 5mm. The yellow/ blue light energy ratio (Y/B ratio) was increased from 0.8 to 2.9 and the efficiency was increased from 86 lm /w to 113 lm /w respectively. The efficiency analysis and prediction method was established based on the experimental data. In order to further increase the Y/B ratio, the double yellow phosphor plates pumped by blue LEDs was investigated. The Y/B ratio was enhanced more than twice to 5.94 and the efficiency was increased to 121 lm /w. The highest efficiency can be achieved to 130 lm / w from optimizing the Y/B ratio. Although the color rendering (Ra = 89) can be effectively enhanced by using single yellow/red mixed phosphor plate ,the efficiency dropped to 68 lm /w. It was attributed to the low energy conversion efficiency of red phosphor and yellow light re-absorption phenomenon. The efficiency analysis and prediction method of remote phosphor structure can provide a quick and convenient estimation of optimum efficiency before experiments.

Keywords: LED, remote phosphor, luminous efficiency