Headlight restoration or plastic headlight restoration is the act of refinishing aged headlight lenses that have become discolored or dull due to oxidation primarily due to UV light and other environmental factors such as road debris impact (stones, sand, etc.) rain, and exposure to caustic chemicals.
...Over time the protective hardcoat breaks down with UV degradation and wear from abrasion, etc. If left untreated the headlights will eventually develop small surface cracks, a condition referred to as crazing. The effectiveness of the headlight in terms of light output measured in lux can be significantly reduced.
This condition which results in hazy and discoloured lenses is known for causing reduced night time visibility for drivers as the condition becomes worse. It is possible for cloudy and hazy headlights to be restored to a like-new condition and represents far more economical alternative than replacing the lens.