基于能量守恒定律和网格划分法，设计了一款用于超薄直下式发光二极管（LED）平板灯的大角度透镜。以朗伯型发光LED在高度为96 mm下的目标面照度分布作为期望照度分布，对大角度LED透镜进行反馈优化，使其在高度为25 mm的目标面上就形成具有期望照度分布的光场。为探究优化后的大角度LED透镜对直下式LED平板灯的厚度减薄程度，将目标面高度分别设为20，25，30 mm，方形LED阵列的间距分别设为96，82，75 mm，利用LightTools软件模拟分析了直下式LED平板灯的目标面照度均匀度。研究结果表明，当目标面高度为25 mm、方形LED阵列的间距为82 mm时，目标面上的照度均匀度最好，其值(照度最小值除以照度最大值)达至0.8756，符合国家LED室内照明应用技术要求。

Based on the law of conservation of energy and the mesh generation method, a lens with large view angle for ultra-thin direct-down LED panel light is proposed. The illumination distribution of the target plane of the Lambertian type LED at a height of 96 mm is used as the desired illumination distribution to optimize the feedback of the large angle LED lens, and form a light field with a desired illumination distribution on a target plane with a height of 25 mm. To investigate the influence of the large angle LED lens after optimization on the thickness reduction degree of the straight down LED flat lamp, the height of the target surface is set to be 20, 25, 30 mm respectively, and then the spacing of the square LED arrays is set to be 96, 82, 75 mm respectively. The software LightTools is used to simulate and analyze the uniformity of the target illumination of the direct LED flat lamp. The results show that when the target plane height is 25 mm and the pitch of the square LED array is 82 mm, the illumination uniformity of the target plane is the best. And the value (the minimum illumination is divided by the maximum illuminance) is 0.8756, which meets the national technical requirements for the application of LED indoor lighting.