Heat Generation by the Phosphor Layer of High-Power White LED Emitters

In phosphor-based high-power white light-emitting diode (LED) emitters, heat is generated by the phosphor layer due to Stokes shift and light absorption. To estimate the heat generation by the phosphor layer, a phenomenological 1-D model is developed and high-power white LED emitters with different correlated color temperatures (CCTs) are measured. The model prediction and experimental data show that, depending on CCTs of emitters, about 25% to 45% of radiant power emitting from the LED chip is converted to heat by the phosphor layer. The volume heating power density in the phosphor layer decreases with its distance to the LED chip, and the difference can be 5 to 15 times between the phosphor layer surface close to the LED chip and that away from the LED chip. It is suggested that the heat generated by the phosphor layer needs to be effectively dissipated in order to improve the lifetime and efficiency of high-power white LED emitters.