针对普通扩散管应用于双端投射发光二极管(LED)日光灯中存在出光效率低等缺陷，研究了一种内表面为三角形微结构、外表面为凹面微透镜结构的扩散管。介绍了双端投射LED 日光灯扩散管原理，给出了扩散管内表面三角形微结构底角计算公式。采用Tracepro 软件仿真分析了扩散管微结构参数对透光率的影响。结果表明：内表面微结构三角形底角确定后，三角形底边宽度D 不会对透光率产生影响；外表面微透镜直径d 对透光率影响较大(当d =D/2 时透光率最低)，而其形状决定扩散角度大小(横截面为样条曲线的凹面微透镜的扩散角大于正圆曲线和椭圆曲线)，但透射率相当。优化后的扩散管透光率约为0.92，其轴向光束角约为180°，径向光束角为360°。采用改进的双三角形内表面微结构可使日光灯管轴向光照度均匀性优于90%。

In order to overcome the defects such as low light emitting efficiency of double-capped cast light emitting diode (LED) daylight lamp using a general diffusion tube, a new diffusion tube with triangular microstructure as inner surface and with concave micro-lens microstructure as outer surface is studied. The principles of such a diffusion tube used for double-capped cast LED daylight lamp is introduced. A formula to calculate triangle microstructure′s base angles is derived. The influences of the parameters of the diffusion microstructure on the efficiency of the transmitted light are analyzed by simulations using TracePro software. The results show that, when triangle microstructure′s base angles are certain, triangular bottom width D has no effect on the light transmittance. Diameter d of the outer micro-lens surface has a greater impact on the transmittance, and the transmittance is the lowest when d=D/2. The shape of the outer micro-lens surface determines the divergence angle of light beam from this diffuser, and the divergence angle for a concave micro-lenses with cross-section being spline curve is greater than that with cross-section being perfect circular or elliptic curve. However，their transmittances are similar. The transmittance of this diffuser after optimization is about 0.92, the axial beam divergence angle is about 180°, and the radial beam divergence angle is 360°. The axial illumination uniformity of the daylight tube is better than 90% when using the improved double triangle inner surface microstructure.