Partially OT: Headlights

My Subaru's have always held up well but I see it is bad on others of much newer vintage and higher cost. Do not know if the lens makers apply them but there are scratch resistant coatings for plastics. Plastics having much lower hardness than glass are more subject to erosion from grit like sand. There are products sold for refinishing these clouded lenses. They clean and perhaps coat. I was familiar with these coatings for acrylics. I mentioned in another thread here that I used to polish the plastic lens on an old watch with toothpaste.

Ultraviolet light damage from the Sun. You'll see anything made of transparent plastic sitting outdoors start to turn yellow. Other non-transparent plastics also start to lose their colours.

Changing headlight bulbs is also pretty cheap and easy, most of the time. Plastic replaced glass specifically because of its fragility and tendency to crack and break. If you don't want your headlights to yellow, then keep your car indoors in a garage.

Yousuf Khan

There are plastics that won't yellow, but polycarbonates are light and cheap and easy to form, as well as being pretty resistant to chipping and cracking. - so we get polycarbonate plastic headlights that check and craze and yellow - but don't breal. I've replaced more headlights for yellowing than I ever replaced for breakage - particularly on "euro" style lamps.

Brief article on plastics used in lenses:

Also mentions coatings used to protect from UV and hazing. These coatings have been around for decades.

Thinking it might be best to use those kits sold in auto stores as besides removing haze which can simply be done by buffing out they may also contain the UV and hazing prevention coatings.

Personally I've had no problem with my Subaru's and am dismayed to see the problem on much more pricey vehicles.