Nanocrystal-filled polymer for improving angular color uniformity of phosphor-converted white LEDs.

Improvement in angular color uniformity is of significant importance to reach high illumination quality for a white LED. In this demonstration, we show potential applications of cellulose-nanocrystal (CNC)-filled polymer for enhancing color uniformity of white LEDs. The excellent optical diffusion capability provided by CNC and the mechanical flexibility offered by the polymer matrix render it a highly efficient color mixer. The CNC-filled polymer was applied on the outer surface of a conventional white LED module to enhance both color and illumination uniformities. It reduced 71.4% of angular color deviation and improved illumination uniformity by 35.5% while maintaining over 85% of light energy transmission. We also demonstrate that for a specific application purpose, such as downlight illumination, one can simultaneously achieve high color uniformity and downlight illumination with reduced glare by constructing the CNC-filled polymer into a CNC-doped lens. In this case, a 0.03%-CNC-filled lens can reduce angular color deviation by 74.0% and achieve a light energy transmission of 85.5%. The light energy transmission can be further improved by advanced lens designs for energy-saving purposes.