针对直下式液晶电视LED背光系统，提出了一种轻薄化的均匀照明设计方案。采用二次曲面光学透镜，可有效避免光学透镜在大角度均匀照明下全反射的发生，且能在目标面达到符合标准的亮度及均匀度。实验结果表明: 采用21颗1 W灯珠，在灯箱高度为25 mm的情况下，背光系统可达到31.5寸液晶电视背光源的亮度和均匀度要求，相对于传统的直下式背光系统，大大减少了器件的使用数量及灯箱厚度，提高了器件的出光效率和系统稳定性。

A design is proposed to achieve the thinner and more uniform illumination for LED direct type backlight system of LCD TV. Based on two free surfaces, the optical lens can prevent total reflection occurs effectively under uniform illumination of wide angle, and achieve the satisfied brightness and uniformity in the target surface. The results of the experiment show that with the 21 LED of 1W in LCD TV boxes of 25 mm height of the case, the requirements of brightness and uniformity of the 31.5-inch LCD TV backlight can be achieved. Compared with the traditional direct type backlight system, the number of LED chip and the height of system is reduced by using the method. Also, the optical efficiency of the device and the reliability of backlight system are improved.