A Transmission-Type Testing System for Measuring Optical Characteristics of Phosphors for Remote-Phosphor-Based White LEDs

In this paper, we have proposed a transmission-type testing system for determining optical characteristics of remote-phosphor plates in white light-emitting diodes (WLEDs). A comparative analysis between the proposed system and a traditional reflection-type system has also been conducted. Results show that the measured optical efficiency of phosphors appears lower for the former than for the latter. Reasons lie in that, for the latter, during measurements, more blue leakage light enters the detector of the system, and more blue light is reabsorbed by phosphor plates and converted to yellow light. Both factors may lead to a slight increase in the light conversion efficiency of phosphors for the reflection-type system. However, in a real structure of WLEDs, the exciting light is mostly transmitting through the phosphor layer rather than being reflected. Finally, we propose that the transmission-type system is more suitable for determining optical properties for remote-phosphor WLEDs.