Study on the effect of the phosphor distribution on the phosphor layer temperature in light emitting diodes by lattice Boltzmann method

The phosphor-converted light emitting diodes (LEDs) are the most frequently used white light LED. Due to the Stoke´s loss, the silicone/phosphor composites generate a considerable amount of heat. However, as a result of different sedimentation times or coating processes, the phosphor particles present different distributions in the silicone matrix, which has been proved to strongly influence the performance and the reliability of LEDs. A lattice Boltzmann model with heat source is established to investigate the effect of phosphor particle distributions on the local temperature in the phosphor layer. The phosphor heat generation was calculated by a modified Kubelka-Munk theory. Simulations were conducted under four different phosphor particle distributions which correspond to four cases: homogeneous distribution, partial sedimentation, complete sedimentation, and remote coating, respectively. Then the temperature fields of the phosphor layer under these conditions were obtained. The minimum and maximum temperatures in the phosphor layer were analyzed to investigate the effect of phosphor self-heating under different phosphor particle distributions. According to the simulation results, different phosphor particle distributions lead to the hotspot location shift and different temperatures. The minimum temperatures were hardly influenced under different phosphor particle distributions, while the maximum temperatures have a difference over 26 K between these different cases. The remote coating brings the highest temperature which reaches 374.049 K and the phosphor sedimentation can decrease the maximum to a certain extent. The phosphor self-heating with different phosphor particle distributions brings obvious influence on LED thermal management.