Abstract
ABSTRACT White LEDs based on UV LED pumping visible phosphors have the advantages of stable color temperature, high color rendition, good color uniformity, easy fabrication, and low cost. However, the electrical-to-optical conversion efficiency is lower than that of the mainstream white LEDs technology based on blue LEDs pumping yellow phosphor. The low efficiency is due to two factors. One is the low efficiency of current UV LED. The other is the low phosphor conversion efficiency. This study proposes a way to improve the efficiency of UV pumped phosphor-converted LED using omni-directional reflector (ODR) film. A one-dimensional model to approximate the light extraction is derived to predict the light extraction and to optimize its design. According to experimental result, the present method using ODR film can enhance the light extraction. Prediction of the proposed model is consistent with the experimental result. The LED using ODR films has higher efficiency with thinner phosphor layer, higher reflectance of bottom-boundary of phosphor layer for UV light, and smaller light absorption of silicone resin. A theoretical maximum improvement of 2.62X is predicted.