Angular Color Uniformity Enhancement for Color-Mixed LEDs by Introducing a Diffusing Coating Layer

In this study, a simple and low-cost method is proposed to enhance angular color uniformity (ACU) of color-mixed light-emitting diodes (cm-LEDs) by introducing a diffuse coating layer. Optical models of the proposed cm-LEDs packaging modules were constructed by Monte Carlo ray-tracing simulation. The simulation results demonstrate the ACU enhancement of the cm-LEDs packaging modules with the application of the diffuse coating layer on the reflection cup. Owing to the strong light scattering and diffuse reflection effects of the diffuse coating layer, the different color light emitted from the different chip are sufficiently mixed. The diffuse coating layer was fabricated by spraying method. Its optical performance was demonstrated by experiments. The correlated color temperature (CCT) deviations of the cm-LEDs applying the diffuse coating layer have been reduced from 1174 K to 138 K at viewing angles ranging from -80° to +80°. A lowest luminous flux loss of 3.54% is obtained. The diffuse coating layer could also maintain the excellent ACU performance when the average CCTs changes from about 2000 K to 5200 K. Extremely small CCT deviations were obtained, which are less than 300 K at average CCTs ranging from 2000 K to 5200 K. The results demonstrate that the diffuse coating layer on reflection cup is a feasible and effective method to enhance the ACU of the cm-LEDs.