A Simple Method to Realize Millilens Array on Encapsulant Layer for Enhancing Light Efficiency of COB-LEDs

The chip-on-board light-emitting diodes (COB-LEDs) present low light efficiency due to the total internal reflection (TIR) at the flat encapsulant-air interface. In this study, a simple method based on complementary printing was proposed to realize the millilens array on the flat encapsulant layer to diminish the TIR effect, and thereby improve the light efficiency of the COB-LEDs. Experiments and optical simulation based on the Monte Carlo ray-tracing method were conducted to investigate the effect of the lens curvature 8, lens radius R, and lens spacing D on the light efficiency of the COB-LEDs. The results show that the light efficiency of the COB-LEDs increases with R and decreases with D, and COB-LEDs with hemispherical lens arrays (8 = 90°) have the highest light efficiency when R and D are fixed. Compared with the conventional COB-LEDs with a flat encapsulant, closely arranged hemispherical lens arrays with an R of 0.5, 1, and 1.5 mm enhance the light efficiency of the blue COB-LEDs by 87.56%, 90.62%, and 95.73% and enhance the light efficiency of ~6000-K white COB-LEDs by 17.24%, 18.86%, and 20.33%, respectively.