Phosphor thermal quenching refers to the reduction in efficiency of phosphors at high operating temperatures. Phosphors are used in white LEDs to broaden spectral power distribution (SPD) by down-converting blue or UV (violet) emission from GaN based LEDs. Due to thermal activation and the release of the luminescent center through the crossing point between the excited state and the ground state, an increase in the temperature at the phosphor/binder layer accompanies an increase in the probability of non-radiative transition. Phosphor thermal quenching leads to lumen degradation and color shift. The temperature at the phosphor/binder layer depends on the heat introduced to the junction by the LED chip, Stokes loss, light absorption, and thermal management.