Before explaining how to restore headlights, I’d like to discuss why and how headlights oxidize and yellow over time. When cars were originally produced, they used glass for headlights and therefore did not deteriorate like today. Due to safety (during and after crashes) and cost, modern headlights are now built using a plastic mold called polycarbonate. It’s very durable and impact resistant, but over time but will oxidize due to the UV rays it endures every day. These headlights will come with a UV coating from the factory that is durable, but only for approximately 8 years or so typically before they inevitably begin to fade.
Once you notice your headlights looking rough and yellow, that means the factory coating is beginning to fail and is no longer offering any protection. The best way to fix this (other than buying a new set of headlights) is to restore them by removing the old, dried coating and applying your own protection.
There are a couple different ways to do this. One is sanding, polishing, and coating the headlights with some form of UV protection, and the other is to sand, polish, and PPF (paint protection film) the headlights. I am only going to talk about coating them in this article.
The tools needed will be various grits of sandpaper (800-1000,1500-2000,2500-3000), spray bottle of water, isopropyl alcohol, microfiber towels, automotive tape, polisher, compound/polish and your choice of protection (sealant or ceramic coating).
First, start by taping the painted areas around the headlight to prevent any damage being inflicted while sanding. Next, you’ll need to remove the old factory coating by using either 800 or 1000 grit sandpaper depending upon the severity of the oxidation. Spray water onto the headlight as you are working in order to help keep the sandpaper clean. Once the entire headlight has a uniform haze from the sanding, you will know the old coating is completely removed. Then move up to your next grit of sandpaper to start refining the deeper sanding marks; then once again with either 2500 or 3000 grit. Wipe the headlight clean of debris for the next step: polishing. Using a compound followed by a polish will allow for the most amount of clarity before applying protection. The last step is to apply your choice of protection. Thoroughly clean the headlight with isopropyl alcohol to remove any polishing oils to allow for the maximum bond of the ceramic coating or sealant.
A sealant can offer some amount of UV protection but will need to be applied frequently; I would apply a sealant at least once a month. A ceramic coating will last much longer than a sealant but still not the same amount as a factory coating. The ceramic coating you choose will determine the longevity, but it can also be maintained with specific ceramic toppers. Either decision will require maintenance of the headlights from now on since the factory coating is removed.