One of the most common questions about composite headlights is asking what can be done to get rid of yellowed, hazy lenses. There are really only two possible solutions: replace either the lens (rare) or entire housing, or polish them.
Before even thinking about polishing, look to see what new lights would cost. In many cases, new light housings are cheaper than the supplies you’ll need to polish them. You’re going to spend several hours polishing, between removing the lights from the vehicle, progressively sanding, polishing, and then clearcoating–it’s a lot of work done right.
If the lights are expensive, and replacement isn’t reasonable, you’ll need to progressively sand the lights. I recommend 3M’s Headlight Lens Restoration System, which is available for around $15 on Amazon, at your local auto parts store, or Wal-Mart, and uses a battery drill to do the heavy work.
After you’ve polished the lights, it’s imperative to clear coat them. Polycarbonate yellows when exposed to sunlight, and all headlights are manufactured with a UV-inhibiting coating, which the polishing process removes. If you don’t replace that coating (and don’t be fooled by wipe-on products) with a high-solids clear coat, you’ll be right back to hazy lenses in a few months.