27.4: Design of Double Freeform Lens for Mini‐LED Backlight Modules

Abstract

Mini light‐emitting diodes (Mini‐LEDs) have been considered as promising light sources for direct‐lit backlight modules (BLU). To achieve uniform illumination, double freeform lenses are usually employed to redistribute rays from Mini‐LEDs. The traditional design method of a single lens under the point light source can achieve high uniformity on the observation plane. However, in the array configuration, especially when the horizontal distance between Mini‐LEDs is not equal to the vertical distance, the uniformity decreases when it is applied under the extended light source. To solve this problem, a lens design method is proposed in this paper to satisfy the requirement on uniformity. Firstly, the illuminance value is numerically calculated based on array configuration and illuminance superposition method. Then we optimize the illuminance distribution curve with the feedback method. A double freeform lens is designed based on the optimized illuminance curve. On the target plane, the simulation results show that compared with the traditional method of lens design, the uniformity improves from 77.69% to 88.03%. The design method is simple, effective, and easy to implement.