New freeform lenses for white LEDs with high color spatial uniformity

A novel freeform lens structure made up of two surfaces is proposed and optimized to enhance the color spatial uniformity (CSU) of white light-emitting diodes (LEDs). Compared with our previous method, an improved design method by optimizing the light energy mapping relationship is proposed to eliminate the dark area, which appears in the illumination pattern due to a deep batwing luminous intensity distribution. Moreover, experiments with a significant evaluation function are performed and demonstrate that the CSU in terms of color difference (Δu'v') can be enhanced as high as 92%. In addition, this novel lens can further improve the CSU of white LEDs with conformal coating. High-quality illumination pattern without yellow rings and dark areas can be realized based on this novel freeform lens with little light loss.