Most automotive headlight lenses made within the last 20 years are made of polycarbonate plastic. Polycarbonate is a clear, hard polymer which is very popular because it allows manufacturers great design flexibility. Unfortunately, polycarbonate, like most plastics, can degrade over time due to UV radiation and become yellow and foggy. This is obviously an undesirable condition because it becomes a safety hazard due to diminished road illumination. The solution is to restore your headlight lenses.
The least aggressive method of restoration is to use an all-in-one (AIO) cleaner. Klasse AIO, Zaino AIO, Poorboys World Polish, or equivalent, may do the trick if the lenses are not too badly clouded. All of these products are applied in a similar way – typically you apply a small amount of product to a foam applicator and work the product until a fresh, clean plastic surface appears.
If using an AIO fails to yield success, you can try a more aggressive plastic polish such as Meguiar’s PlastX, 3M Plastic Cleaner, Mothers Plastic Polish, etc. Most of these products contain ultra-fine abrasives that work to remove the top film-like layer of the lens. Using a plastic polish is quite straightforward and can be done by hand or with an orbital buffer…using a buffer will provide the best results.
Wet-sanding/polishing is the most aggressive method you can use. You will need some fine-grit wet/dry sandpaper. Fill a bucket with some water and soak the sandpaper in the bucket for about 15 minutes prior to starting. Take the sandpaper and sand the lens, side-to-side, applying light to medium pressure.
At this point, you will need to polish the lens with a buffer to remove the sanding marks…don’t attempt to polish the lens by hand. An orbital buffer is best. When you are finished polishing, wipe with a towel to assess progress…you will most likely have to polish a second time, or third time.
It may take some time but your lenses will likely polish to a nice, clear finish. Keep at it if this doesn’t seem to be the case, it may take 15-30 mins per lens. When you are done, you should have lenses that are just as clear as new. Job well done!