[///MPhatic]

Originally Posted by chris719

They aren’t UV coated, it’s actually UV inhibitor mixed into the plastic.

That's interesting. Every newer car I have owned had the UV coating added onto the outer part of the lens, including my '18 Lexus IS350.

[chris719]

Originally Posted by ///MPhatic

That's interesting. Every newer car I have owned had the UV coating added onto the outer part of the lens, including my '18 Lexus IS350.

People have claimed for years and years that headlights are coated from the factory but I can't find any evidence that they actually are. It actually doesn't make sense to coat them because it's another manufacturing step and you can easily mix this stuff into the plastic. I haven't dealt with headlights but in medical we use a lot of clear polymers and almost always have UV inhibitors mixed in. Now, the UV stabilizers can also migrate over time to near the surface so that can be why they appear to oxidize faster after polishing.

[///MPhatic]

Originally Posted by chris719

People have claimed for years and years that headlights are coated from the factory but I can't find any evidence that they actually are. It actually doesn't make sense to coat them because it's another manufacturing step and you can easily mix this stuff into the plastic. I haven't dealt with headlights but in medical we use a lot of clear polymers and almost always have UV inhibitors mixed in. Now, the UV stabilizers can also migrate over time to near the surface so that can be why they appear to oxidize faster after polishing.

I'm here to tell you that without question many are. I've refinished 10+ sets of headlights myself, the coating comes off, they look brand new, and 3 months later you have to redo it all over again because the UV is gone, which then yellows/fades the housing.

Do some research on it, there are thousands of examples. The number of YouTube videos showing how to fix the issue is staggering because it's so pervasive.

[chris719]

Originally Posted by ///MPhatic

I'm here to tell you that without question many are. I've refinished 10+ sets of headlights myself, the coating comes off, they look brand new, and 3 months later you have to redo it all over again because the UV is gone, which then yellows/fades the housing.

Do some research on it, there are thousands of examples. The number of YouTube videos showing how to fix the issue is staggering because it's so pervasive.

Like I told you, even if UV inhibitors are mixed into the plastic they tend to migrate to the surface just like the plasticizers, which fully explains that behavior. Also, like I said, the UV inhibitors are consumables and once your headlight is oxidized it's already gone. I don't need to do research on it. I'm speaking to how things actually work from some limited plastic manufacturing experience, not what YouTubers and random internet sources repeat as truth.

https://weeklypellet.com/2019/11/13/...bonate-and-uv/

There’s even materials specifically made with UV stabilizers to meet federal standards for automotive.

As you can see, this plastic for headlight lenses is infused with UV stabilizer:
https://solutions.covestro.com/en/pr...78848-00009654

I prefer fact to anecdote.

[///MPhatic]

Originally Posted by chris719

I prefer fact to anecdote.

You might want to know every manufacturer's process before you go there, and the fact is, you don't.

[chris719]

Originally Posted by ///MPhatic

You might want to know every manufacturer's process before you go there, and the fact is, you don't.

Difference is, I know they buy raw plastic with UV stabilizers/inhibitors already in them because the only plastics that meet SAE J 576 have them, and that is a standard referenced by 49 CFR 571.108 that is a US regulatory requirement. Do they also use a top coating? Maybe, maybe not. It’s certainly nothing you can see or determine on your own.

Feel free to ignore the fact that even if there is a top coating, its UV inhibitory capabilities are exhausted if the headlight lens needs polishing in the first place.