[gblargg]

A big cause on older cars is haze on the clear plastic that develops over the years. This makes even low beams spread so they blind oncoming drivers. There are kits where you polish and re-finish them, and they do make a noticeable difference in beam directionality.

[branko_d]

According to Project Farm, Sylvania is the best headlight restoration kit:

https://www.youtube.com/watch?v=kyVCEbfrU-c