Enhancing angular color uniformity of white light-emitting diodes by cone-type phosphor layer geometry

Angular color uniformity (ACU) is an important optical parameter for phosphor-converted white light-emitting diodes (LEDs). The phosphor layer geometry usually presents the spherical-cap shape by the conventional dispensing coating method, thus yellow ring phenomenon appears in the radiation pattern and leads to poor ACU. In this paper, a kind of cone-type phosphor layer geometry was proposed to enhance the ACU of white LEDs. Optical simulations were performed by the Monte Carlo ray-tracing method. Results show that the proposed cone-type phosphor layer geometry has significant positive effect on enhancing the ACU of white LEDs. Compared to the conventional phosphor layer geometry of spherical cap with the same volume, the ACU is increased by more than 19% by the cone-type phosphor layer geometry. With the same correlated color temperature (CCT) and phosphor concentration, the ACU is increased by more than 20% and the phosphor layer volume is reduced by more than 4.5% to save material cost.