Yellowing headlights is something very common in cars. Not only do they look unappealing, but they also have a very poor light output on the road at night making night driving difficult and risky.
How does this happen?
The lens on the headlights are made of a polycarbonate plastic and even though it is not visible to the naked eye, this comes automatically from the factory with the UV protective coating. Over time, UV rays (especially in Australia – thanks Ozone Layer!) coming from the sun breaks down the polycarbonate structure in the lens triggering the discoloration from transparent to yellow.
Headlights restoration should be done as quickly as possible because over time the damage can spread deep into the lens and create little cracks known as crating’s. If left untreated, cracks will get bigger and eventually destroy the lens. In this event, it can really hurt the hip pocket as buying new headlights is expensive.
How to Repair:
Rinse the headlight and the surrounding area using a microfiber towel to remove any dirt. Then dry the headlight. Next you will be removing the top layer of yellowing plastic on the lens.
To do this, you can use:
- A cutting compound.
- Metal polish (which are liquid abrasives).
- Wet & Dry sandpaper – multiple grits required.
All these products contain aluminum oxide as the abrasive agent in different amounts. Up to 5% in polish, up to 10% in compound, up to 25% in metal polish and (of course) up to 100% in sandpaper. With the sandpaper, the higher the grit number the finer the grit. It is important to choose the right polish and the right sandpaper when restoring headlights.
The reason this is mentioned is because when restoring your headlights it is important to use the right polish and the right sandpaper.
For yellowed headlights, it is best to start with 600 grit, followed by 1500 grit, followed by 3000 grit.
If using your hands use a foam backing pad for abrasives sheets. So, you can put the uniform pressure on the lens as you sanding.
If you are using a drill or polisher, for a headlight polishing kit. Get a backing plate for the drill, a wool pad, a foam pad and sanding discs.
Next mask of the surrounding body panels using some masking tape. This is to protect the surrounding panels while sanding.
Then spray some water on the lens and on the sandpaper and start sanding. It is best to do this sanding in one direction, for example horizontally with overlapping passes to cover the entire area of the lens. Spray more water, keep sanding with light pressure on the sandpaper. When the water the lens turns from yellow to sort of milky white. Wipe the lens, you will now see the yellow on the plastic is gone but there is now a white haze on the lens. These are scratches from the 600 grit sandpaper.
To remove this, grab the 1500 grit sheets and start sanding again. This time instead of going horizontal vertically, this will remove the horizontal scratches a little easier. Once you have done the entire lens, wipe the lens again and now you have an even finer haze from the 1500 grit. Which may be hard to see.
Now grab the 3000 grit and do this one more time in the horizontal strokes to remove the vertical scratches. Repeat the process.
Next up, the compound. For this, you can use a microfiber towel but this will take a fair bit of elbow grease.
We suggest using a drill/polihser because it is much quicker, if you have one you will also need a wool pad. Apply some compound on the pad and then remove the tape and start buffing. Maintain a consistent speed with a uniform pressure on the pad while keeping the pad flat against the headlight and keep the pad moving to avoid heat buildup and burning the plastic. Cover the entire area with horizontal overlapping passes and then switch to vertical passes and cover the entire area again. When completed, wipe the lens.
If would like to go one extra step, switch to a foam pad. By doing so and using some polish it will bring back the that factory shine you once had. This is completely optional.
There you go, clarity is back just like in a brand new headlight. That's how you restore headlights with very bad yellowing which require using sand paper.
Headlights with Only Minor Yellowing:
If you only have minor yellowing, you can skip all the sanding work and start out with the compound.
There are many good headlight restorer products available. Simply add some compound on the pad and start buffing and buffing and buffing…..until the headlight starts to look really clean. Wipe the headlight down. To finish you can use isopropyl alcohol to remove any leftover compound.