The clarity of even new plastic headlights can deteriorate within a couple years after being manufactured and installed on your automobile. Time and use will cause dimming of the light output. This makes driving at night unsafe as it diminishes how far forward your headlights project their light. Many of these headlights can cost $500-$1500 each to replace, and that’s just for the lens and doesn’t include labor. What happens is headlights become foggy. This is because the clear coating applied at the factory begins to degrade due to UV breakdown and sand and grit abrasion.