Modern automobile manufacturers use moulded polycarbonate (plastic) headlight covers to protect the headlight bulb and reflector inside the headlight housing. Ultraviolet rays from the sun degrade the plastic and cause yellowing over time. Driving in sandy, dusty or salty areas will cover the headlight with a patina of scratches. This type of damage causes the headlight to lose apparent brightness and reduce visibility due to the decreased amount of light penetrating the cover. Polishing the headlight covers will remove the damage and restore the headlights to full functionality.
Mask off the headlight from the surrounding painted areas with painters tape. Tape right up to the edge of the headlight cover and do not leave any paint uncovered.
Clean the headlights with a soft rag and water. Remove any dirt or bugs that may be stuck to the headlight.
Wrap a piece of 600-grit wet-or-dry sandpaper around a soft sanding block. Wet the paper and block with clean water. Sprinkle clean water onto the headlight.
Sand the headlight lengthwise with long, uninterrupted strokes. Sand the entire surface until it has a uniform foggy appearance. Rinse the headlight with clean water. Repeat until all the deep scratches and pits are gone.
Wrap a piece of 1500-grit wet-or-dry sandpaper around a soft sanding block. Wet the paper and block with clean water. Sprinkle clean water onto the headlight.
Sand the headlight with strokes 90 degrees from the first strokes. Sand across the scratches from the first pass until they disappear entirely. Rinse the headlight with clean water.
Wrap a piece of 2000-grit wet-or-dry sandpaper around a soft sanding block. Wet the paper and block with clean water. Sprinkle clean water onto the headlight.
Sand the headlight lengthwise with long, uninterrupted strokes, 90 degrees from the second sanding direction. Sand across the scratches from the second pass until they disappear entirely. Rinse the headlight with clean water.
Apply buffing compound with a soft rag. Rub the headlight with the rag in a circular pattern while moving across the surface. Buff the headlight, rinse with clean water and inspect it for cloudiness. Repeat until the headlight is clear.
Apply a coat of plastic polish with a soft, clean rag. Buff the polish until the headlight is shiny and clear.
Remove the painters tape. Wipe down the area to remove any residual plastic dust or buffing compound with a clean rag.
Keep the sandpaper wet during the sanding. The water cools and lubricates the grit while carrying off the plastic dust that will clog up the sandpaper and reduce its effectiveness. Treating the headlights with a good plastic polish with UV inhibitors in it will help preserve the covers and prolong the intervals between polish jobs. Kits by several manufacturers are available for sale with the sandpaper and polish included. These kits are good for folks who prefer to use power tools. Look for headlight cover polishing kits in auto-part stores and in the automotive department of large retail stores.
Don't over-sand the plastic. The first sanding removes the pitting, scratches or discolouration. Subsequent sanding progressively removes the grooves left by the coarser sandpaper, until the plastic is clear and smooth. Over-sanding with any one grit of sandpaper could damage the plastic cover or create unnecessary work for you.