Headlight lens cleaning/polish

[Harry Bloomfield]

Might it be less a case of UV breakdown, and more a case of oxidation?

Yes, possibly - I hadn't thought/expected that of a plastic. Everyone has always suggested it is UV breakdown, so I accepted it.

[EDIT] A bit of digging in scientific papers, suggests polycarbonate is susceptible to both UV and oxidation when exposed.

 

[Brigadier]

Yes, possibly - I hadn't thought/expected that of a plastic. Everyone has always suggested it is UV breakdown.

One of a number of ways that a plastic can degrade, although UV is the go-to thought in most cases.

Certainly, it would offer an plausible explanation for your "clouding headlights when not UV-exposed for prolonged periods of time" situation.

 

[Brigadier]

Perhaps then (on the understanding that polycarbonate can degrade by chemical, UV, or oxidation, for three), the best way to avoid clouding headlights is to clean them regularly, keep them clean, and reapply protective lacquer whether you think they need it, or not?

 

[DIYspanner]

Managed to get some clouded headlights on a VW Bora clear using wetNdry, finish off with a buff with glass polish.

Started off with 500 wetNdry and worked up in 500 increments to 3000 grit. Finally, the glass polish. Probably better if you can remove the headlights to do the job so none of the paintwork accidentally gets scratched.

 

[EddieM]

Here comes the science. The double bond of carbon is at an energetic level that UV is at a compatible level to destroy. (That was really badly worded)

 

[Harry Bloomfield]

Here comes the science. The double bond of carbon is at an energetic level that UV is at a compatible level to destroy. (That was really badly worded)

Well then, try again - I'm interested.

 

[EddieM]

Well then, try again - I'm interested.

Ok C=C chemical bonds are susceptible to being broken by UV. Polycarbonate has 6 such bonds.