Polycarbonate (PC) and polymethyl methacrylate (PMMA) are the preferred materials for lighting applications due to their high transparency and excellent mechanical performance. However, neither PC nor PMMA are completely suitable for the waveguides installed in specialized positions, which require a superior thermal stability, high transparency and low absorbance of visible light, especially in the blue light spectrum region (280–450 nm). This report details the preparation of PC/methyl methacrylate (PC/MMA) composites and the subsequent investigation of their composition, homogeneity, and optical properties by scanning electron microscopy, gas chromatography–mass spectrometer and ultraviolet spectroscopy. Furthermore, the mechanical and thermal properties of these composites were investigated according to ISO testing methods. It was found that the composite material consisting of 100 parts PC and 0.05 parts MMA (parts per weight) exhibited an excellent transparency and a high optical energy gap (Eopt) in the blue light spectrum region (280–450 nm), while retaining the high heat resistance and excellent mechanical performance of PC. The potential of this PC/MMA composite, which is intended to address the issue of yellow light emitted from the PC waveguide owing to its superior optical properties, was practically demonstrated.