Car Headlight Restoration 101
Most cars that are even a few years old can have yellowing and cloudy headlights from weatherization and sunlight. Sunlight is bad for you as a person, so you use sunscreen. Sun is bad for your car's plastic headlights because they chemically alter it and yellow. This gets worse until it is cloudy. The net result is that your headlight projection beam at night is greatly reduced and dispersed. Besides, they ruin the look of the car.
All headlight restoration kits are similar. They range from $10-30, on average. All have sandpaper with grit of mostly 1000, 1500, 2500, but they do vary. The higher the number, the smoother the finish will be. Lower grit numbers will help remove tougher oxidation issues . Headlights sooner or later will lose their UV protection. If you fail to replace the UV protectorant after you have restored them, in time, it will happen again. All kits have some sort of sealant or polish. However, not all have UV fluid-the shield against the sun, which causes it.
So, make sure your kit has UV protectorant included, either in a bottle or within a polish. That is the main difference in the restoration kits. For most, you apply some oxidizer to soften the hard film, use sandpaper to rub it off, using lower to higher grit, then final polish and seal. Most of the time, it takes one hour to do both headlights.
I have used carburetor cleaner to remove grime and some yellowing. Others have suggested brake cleaner\fluid. If it is not too bad, it may work to make the job easier.
The 3M and Sylvania restoration kits have consistently received the highest feedback. The Sylvania kit comes with the critical UV fluid also. The 3M does not, although it might in the final polish. Both are about the same price, but 3M is a little cheaper.