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. Fortunately, there are plenty of products on the market designed to help you restore your car's 20/20 nighttime vision. Here's how to clean your headlights so they shine like new.
Most cars and a lot of trucks today are manufactured with headlamp assemblies that use quartz-halogen bulbs plugged into the back of a large plastic reflector. The outer surface of these headlamp modules is molded polycarbonate plastic. That plastic is much lighter than glass and far more resistant to stone chips and cracks. However, after a few years of exposure to sunlight and atmospheric chemicals, polycarbonate has a tendency to get hazy. Severely neglected lenses can actually pit and develop a network of fine cracks, called craze, which makes the job of fixing them tougher. It's worth a shot, though—and you'll need only a few bucks' worth of materials to get the job done. Sure, these assemblies are easy to replace, but they can be very expensive. A pair of lenses for a luxury car can cost as much as a thousand dollars. Woof.
Fortunately, there's a simple and inexpensive solution. Unlike glass, the polycarbonate plastic can be polished back to a surface as smooth as new, in a procedure that won't take more than a half-hour. Check out our list of the best headlight restoration kits.
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.
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.
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.
Source : http://www.popularmechanics.com/cars/how-to/a10346/how-to-make-your-headlights-shine-like-new-16649941/