Influence of Aluminum Coating Thickness on Automotive Lamps

Automotive lighting devices with reflective surfaces require high reflectivity for light collection and optimum photometric efficiency. The reflective surface is commonly aluminum applied by physical vapor deposition (PVD), i.e. an evaporative process or sputtering. The design and process of some reflective surfaces are such that certain areas of the target do not receive sufficient aluminum coating thickness. Reduced coating thickness results in decreased optical efficiency, and has led to increased thermal demands on the thermoplastic substrate. This paper seeks to quantify how reflectivity and substrate temperature are dependent on the thickness of the PVD metal coating, and thermal simulation tools are used to predict lamp temperatures for varying coating thickness of the reflective surface.