The good news about headlight lenses is that they are correctable. Cars were originally built with glass headlights that were easily broken. Most vehicles built since 1990 have polycarbonate lenses. This is a type of clear plastic that bounces back from considerable impact, making it an ideal choice for the front of a vehicle. The problem with polycarbonate is its tendency to yellow and cloud over time as a result of UV exposure. Fortunately, a number of products have been formulated to remove this haze and clarify damaged lenses with minimal cost and effort. In most cases, replacement can be avoided.