Over time your car's headlights haze or fog over due to sand, grit, and other debris literally sandblasting the headlight. Defogging your car's headlights will improve both the light's appearance and function. Buying a wet-sanding defog kit works well, but you can also do the job with denatured alcohol (methylated spirits) and some elbow grease.
Defogging headlights consists of removing the scratches that have been sandblasted onto the surface of the headlight. You can do this by wet-sanding the surface or using denatured alcohol to strip away and polish out the scratches. A user on Mazda forum MX6.com tried both approaches side-by-side and both seemed to work equally well. We've covered methods using toothpaste (polishing) and sandpaper (sanding) in the past, but these are both worth considering as well.
The wet-sanding method involves washing the headlight with water and soap, using masking tape to protect the paint around the light, sanding with an abrasive compound, buffing, and finally polishing the headlight. You can do this by hand, using a drill or rotary tool, or even an orbital sander.
The polishing method requires meths, sold in any home improvement store in the painting section. This method is a lot less complicated -- just use a rag soaked with it to firmly polish the headlight several times. The light may still look foggy while the liquid is on the surface, so after you polish the light for a few minutes take a break and let the alcohol evaporate. You may have to do this two or three times to get the headlight sufficiently defogged.
Whichever method you choose, defog your headlights once every year or two for both good looks and maximum visibility.
Defogging Car Headlights [CarPart4U]