Improvement in angular color uniformity of white light-emitting diodes using screen-printed multilayer phosphor-in-glass.
Angular color uniformity (ACU) is a key optical property of white light-emitting diodes (WLEDs) and high ACU is strongly demanded in illumination applications. In this paper, a multilayer phosphor-in-glass (PiG), which can be produced by the screen-printing method, is proposed to improve the ACU of LED packages. The screen-printing method provides a feasible scheme to produce multilayer, various-shaped PiG with a controllable pattern. Angular correlated color temperature (CCT) distributions of the LED packages with multilayer PiG are simulated numerically and measured experimentally. Optical performance of the LED package with optimized three-layer cone-shaped PiG is compared with that of packages with two-layer and one-layer PiG. The experimental measurements indicate that the deviation of angular CCT can be reduced from 761 to 171 K by cone-shaped PiG at average CCT of 6000 K. The results demonstrate that higher angular color uniformity can be achieved by LED packages with multilayer cone-shaped PiG.