Beyond the modern design and illumination quality of automotive lamps, thermal management plays a crucial role and must be fulfilled in the early stages of the design process. An excessive thermal radiation from incandescent bulb can cause a severe thermal degradation of plastic parts such as housing or optical lens. Hence, to assess such impact of heat on the plastic parts, thermal analysis of a license plate lamp was investigated by a proposed technique combining computational fluid dynamics (CFD) and ray tracing mapping method. Then, the accuracy and computational cost of the method were compared with thermal results obtained by another thermal radiation model using Monte Carlo (MC) technique for calculating radiation effect coupled with CFD in heat transfer analysis. Finally, a comparison of temperature results from both techniques were validated with practical thermal measurements of license plate lamp prototype. This study shows that the proposed methodology gives a sufficiently accurate temperature distribution and can reduce the computational time during product design and development process.