Most headlights are made of polycarbonate plastic, which is durable and scratch-resistant. But over time polycarbonate clouds over, mostly due to UV rays that degrade the outer layer of plastic.
1. Wash Your Car
Wash your car to remove any surface dirt. Waxing it, at least within a foot or two of the headlamps, is a good idea, because drips and droplets of the abrasive polishing compound are less likely to adhere to a freshly waxed surface.
2. Mask Off
Head out to the store and buy some blue, low-tack painter’s masking tape, the handy stuff that peels off easily. Mask the area around the headlamp that needs to be polished. For some reason, the red, yellow and clear lenses for the marker and backup lights, which are molded of ABS plastic, don’t seem to haze as much as polycarbonate headlamps, so you can probably just mask them as well. You may want to remove nearby trim, especially chromed metal or chrome-finish plastic, because we’ll be polishing and sanding with materials that can destroy the chrome.
3. Sand them
All of these products use an abrasive such as sandpaper to scuff away the outer layer of haze. This is the most important step, so be thorough. When you’re done, the entire headlight should be clear of any yellowing and have a rough, dull surface. Soak a piece of 1000-grit wet/dry sandpaper in cold water for 10 minutes. Lightly sand the lens in straight strokes. Methodically cover the entire lens surface, always sanding back and forth in one direction. Keep the surface wet while you work. Again, be careful not to damage nearby paint or trim. Use the palm of your hand to conform to the curved surface of the lens.
Sand until the pits, discoloration and scratches you’re trying to eliminate are gone. Don’t rush this part. And don’t be afraid to dry the surface with a towel and check the uniformity of your sanding. When you’re done, clean and dry the area.
Now perform the same operation with 1500-grit wet/dry sandpaper, this time sanding at right angles to your previous work. Again, be methodical. Keep the paper wet, cover the entire surface and then clean up to remove any abrasive powder. Repeat the procedure, every time at right angles to the last sanding, with 2000-, 2500- and 3000-grit wet/dry. Clean up one last time. You might want to touch up or redo the masking tape along the way if it starts looking a little tattered.
4. Polish them
A fine polish cleans up the sandpaper scratches and makes the headlight lenses clear again.
Let’s assume your lens is only moderately obscured. Start the repair with polishing compound and a flannel or microfiber cloth. Smear some compound on the lens and polish in a circular motion. As the polish gets ground into the cloth and dries out, it lifts the haziness right off the lens. Most of the compound eventually winds up on the cloth, but it probably takes about 10 minutes of rubbing per lens, so don’t be in a rush. If you have an orbital polisher, you can use that with a lambswool or terry-cloth pad. Don’t polish the paint off nearby surfaces. Simply proceed with compound until the lens is shiny.
Okay, you’ve been polishing one corner of the lens for a few minutes, and it’s better—but not perfect. The lens surface is far too degraded for the polishing compound to rescue it. There are still pits that you can feel and see.
Clean up every last vestige of the abrasive polishing compound. Now wax the lens thoroughly with a paste car wax. This last step will keep acid rain, dirt and road salt from attacking the plastic, at least for a while.
5. Apply UV Sealant
There’s a reason we tested only headlight lens restorers with a UV protectant. The sanding step removes any protective layer that was originally applied to the headlight, and if you don’t reapply that shield your lights will haze over again in as little as a few weeks. Some products, such as the ones from Sylvania and Lenz Solution, promise extended protection.