Light extraction enhanced white light-emitting diodes with multi-layered phosphor configuration

Phosphor-converted white light-emitting diodes (LEDs) with separate red and yellow phosphor layers are investigated under current regulation conditions. This novel packaging scheme of bi-layered phosphors leads to more than 18% increase in luminous flux compared to conventional random mixed phosphor case at the same correlated color temperature. Lower junction temperatures of bi-layered phosphor white LEDs are also observed. This advantage in the thermal characteristics is due to the reduced back reflection of light inside the packages. It is also found that the phosphor conversion efficiency of bi-layered phosphor scheme is higher than that of mixed phosphor case. This is attributed to the enhanced light extraction from the LED packages. In addition, the chromaticity coordinates shifts compared bi-layered phosphor with mixed phosphor white LEDs are almost the same under current regulation conditions. The technology of bi-layered phosphor white LEDs with high efficiency and high color rendering index provides an appropriate solution for general white LED lighting. (C) 2010 Optical Society of America