Enhanced Luminous Efficacy of White LED with Flat Dual-Layer Remote Phosphor Structure

Abstract

This paper shows the differences in luminous fluxes of two distinguishing dual-layer remote phosphor structures, Flat Dual-Remote Phosphor (FDRP) and Concave Dual-Remote Phosphor (CDRP). The impact of the distance between the two phosphor layers (d1) and the distance from the phosphor layer to the LED surface (d2) on the optical properties of the CDRP is also presented. Specifically, when d1 and d2 are varied, the scattering and absorption characteristics of the remote phosphor layer change dramatically, which enormously influences the color uniformity and illumination capability of WLEDs. The concentration of YAG:Ce3+ phosphor also needs to be modified so that the correlated color temperature of WLEDs could be maintained at 8500 K when d1 and d2 are adjusted. In case d1 = d2 = 0, the scattering and absorption in the remote phosphor layer are minimal, leading to the infinitesimal color and luminous flux. When d1 and d2 get bigger, the scattering surface increases and that the blue and yellow rays are blended becomes more uniform, leading to the minimum white light deviation as well as the lowest luminous flux. According to the studied results, the lumen output can be maximum at 1020 lm if d1 = 0:08 mm or d2 = 0:63 mm while the smallest color deviation occurs when d1 = 0:64 mm or d2 = 1:35 mm. Therefore, the researched results will provide further information for choosing the suitable d1 and d2 in order to improve the quality of WLEDs.