Abstract <p>Automotive projector headlamps can experience intense local heating when incident sunlight is concentrated by the lens onto nearby polymer components, potentially causing discoloration, deformation, coating degradation, or material softening. Sun load analysis helps to prejudge and mitigate risk of such failures. Reliable prediction of solar-induced hot spots during the design stage remains limited in the open literature, where optical assumptions are often simplified and comprehensive thermal coupling is rarely validated against standardized automotive tests. To address these limitations, the present work evaluates solar loading using the worst-case irradiance levels of 971 and 1012&#xa0;Wm⁻² under controlled relative humidity of 50–98% RH. A modeling framework is developed to predict hot spot temperatures under standardized solar loading and is experimentally validated. The irradiance and incident orientations identified through optical assessment are imposed in a coupled thermal model resolving solid conduction, buoyancy-driven natural convection, and radiative heat transfer using the surface photon Monte Carlo method. Experiments are conducted in a metal halide solar chamber, where a custom alignment fixture reproduces the numerically defined solar orientation, and thermocouples placed around the focal region record hot spot temperatures. The predicted hot spot temperature agrees with experiments within 6.39%, and the simulated hot spot location matches the observed focal region. This validated methodology provides a reliable tool for assessing polymer susceptibility to solar-induced thermal damage, enabling early design decisions, reducing dependence on iterative physical testing, and supporting optimization of lens geometry, material selection, and shielding strategies to mitigate overheating, ultimately improving headlamp quality and extending component lifespan. The details of the study are explained in graphical abstract.</p> Graphical abstract <p></p>