I can’t seem to find my before and after pictures of my son’s Camry. Believe me, it looked horrible. Now he is happy as a clam :bounce , cause his headlights actually reach pass his front bumper. Depending on how thick is the plastic & how bad is the yellowing crust on the lens, you can:
sand it down (trust me it works :secret ), with 800, 1500 and then 2000 grit sand paper using an orbital sander and water. Just make sure the residue that comes off during sanding becomes white instead of yellow and you are not too aggressive with 800 grit. Then, buff it couple of times with whatever fine abrasive you have, I used “Meguar’s Dimond Cut compound 2.0 “ that’s what I just had in my garage & suspect that any fine abrasive like Plast X including cheap toothpaste (assuming it contains most “sand� ) will work just as well.
If it too much trouble removing the headlights from the car and doing it on the bench, you can mask the car around the headlights ~ 8-10� and do it right on the car, just watch for paint….
Don’t forget to apply some kind of wax on the surface of the headlight afterwards, because that’s what will protect it in the future and reapply it each wax you do on the car. I use polymer wax like TW – F21, but I doubt it matters as long as it bonds to the plastic.