Most automotive headlight lenses made within the last 20 years are made of polycarbonate plastic. Polycarbonate is a clear, hard plastic which is very popular because provides a strong protective shell for a car’s internal headlight bulbs. Unfortunately, polycarbonate, like most plastics, can degrade over time. When polycarbonate degrades it turns cloudy and yellow. In this article, we will attempt to understand why headlamp lenses degrade over time and describe some methods to restore them to like-new condition.
Why do headlamp lenses get cloudy?
The main reason headlamp lenses get cloudy is due to their interaction with ultraviolet (UV) radiation from the sun. There are certainly other factors that contribute to lens degradation too, such as exposure to exhaust, salt, grime, oil, acid rain, etc.
Why is UV light so bad? Thomson of Thomson, GA, a full-service Dodge, Chrysler, Jeep, Ram dealer, says It has to do with the fact that the energy of UV radiation is close to the “disassociation energy” of the chemical bonds in the plastic; over long periods of time, the UV radiation causes the bonds to fall apart and this causes the lenses to become cloudy.
Restoring polycarbonate
Headlamp restoration is not too difficult provided you have the right products and equipment. Here we discuss three methods, from least aggressive to most aggressive, that should allow you to restore headlamp lenses to like-new condition.
Method 1: Using an all-in-one cleaner
The least aggressive method of restoration is to use an all-in-one cleaner. Some consist of a solvent only while others consist of a solvent with a mild abrasive. A popular one is Poorboy’s World Polish which is available at most auto parts stores. All of these products are applied in a similar way – typically you apply a small amount of product to a foam applicator (supplied) and wipe the lens until a fresh, clean plastic surface appears.
Method 2: Using a plastic polish
If using an all-in-one cleaner fails to yield success, you can try a dedicated plastic polish such as Meguiar’s PlastX, 3M Plastic Cleaner, etc. Most of these products contain ultra-fine abrasives that remove the top film-like layer of your lens to reveal the clear plastic below. Using a plastic polish is quite straightforward and can be done by hand or with an orbital buffer.
Method 3: Wet sanding and polishing
Wet-sanding/polishing is the most aggressive method you can use and it will take some time. If wet sanding and polishing does not work then you will probably have to replace your headlamp fixture. You will need some fine-grit wet/dry sandpaper (1000 and 2000 grit). Fill a bucket with some water and soak the sandpaper in the bucket for about 15 minutes prior to starting.
Take the 1000 grit sandpaper and sand the lens, side-to-side, applying light to medium pressure. After this, take the 2000 grit sandpaper and sand the lens top-to-bottom, applying light to medium pressure – what you will notice is that the lens will appear to clear up a little. This is due to the finer grit sanding.
At this point, you will need to polish the lens with a buffer to remove the 2000 grit sanding marks…don’t attempt to polish the lens by hand. An orbital buffer is best. Start with the more aggressive polish/pad combo and polish the lens thoroughly. When you are finished polishing, wipe with a towel to assess progress. You will most likely have to polish a second time – once you are complete, move on to the less aggressive polish/pad combo.
It may take some time but your lens will likely polish to a nice, clear finish. Keep at it if this doesn’t seem to be the case. It may take 15-30 mins per lens.
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