Nowadays, Light-Emitting-Diodes (LEDs) are solid-state lighting sources that play a very important role now and future. Many traditional light sources are gradually being replaced by LEDs sources. In order to illuminate light from the new LED source on the desired illumination, the secondary optics have been used widely in LED illumination. Proper illumination can enhance lighting efficiency, uniformity and be suitable for human feeling as well as aesthetic factor. Moreover, an effective illumination can represent lower energy consumption. Therefore, the improvement of illumination efficacy plays important role in the secondary optics system. This book is to investigate the effects of injection molding parameters on mechanical properties and optical properties of PC/PMMA blends. Mechanical properties can be first predicted by some models based on rules of mixture and then verified by experiments. Optical properties are also designed and confirmed by LED lens of injection molding. The ANOVA tables have been finished for determining the significance of injection molding parameters. Illumination testing of TIR lens made of PC/PMMA blends has been proceeded.