You can use sandpaper, but remember sandpaper scratches. If your lens has heavy/severe discoloration with apparent scratches/imperfections, this requires a rougher grit sandpaper, like the 600 grit. If the headlight lens has light discoloration with no apparent scratches, start with at 2500 grit. Whichever grit you use, you want to wet the sandpaper in a bucket or cup of soapy water. [5] X Research source Wet the rag with a commercial plastic lens cleaner or degreaser. Make sure you wet the rag instead of spraying the headlight; this keeps the spray from getting on the paint. Wash the lens with a clean rag or a shop towel.
Dip one finger into a plastic polish or a compound designed for plastic. With the lens still wet, apply the polish evenly over the entire headlight. Grab a sanding sponge or a soft hand pad and take out the starting sandpaper which you decided earlier, in most cases, the 600 grit sandpaper. Fold the sandpaper in three around the Soft Hand Pad Or Sanding Sponge. Dip the sponge and sandpaper into the soapy water. Sand, using a side to side motion, applying even pressure, periodically wetting the sponge and the sandpaper in the soapy water. (Avoid contacting paint and other surrounding surfaces. )
Continue the sanding process using a 1200 grit paper, then even finer 2000 grit and finally 2500 grit sandpaper to remove scratches left by the previous grit. Apply the plastic polish/ compound after sanding with the 2500-grit sandpaper. This time, let it haze, then buff/wipe off with a shop towel. Clean the lens with a plastic lens cleaner or soap and water. This is to remove any polish residue.
Seal the lens with wax or silicone sealer. Fold a shop towel into four and squeeze a quarter-sized amount of wax or polish onto it and let it soak in for a few seconds. Apply to the lens using a single stroke going from left to right gradually working your way down the entire lens.
Be careful and consider masking tape and plastic sheet over the other surfaces to be protected.
