the long term solution ( so I have read) is that because polishing takes off the uv protection layer on the plastic they need a clear lacquer reapplying. Polishing will obviously work but will need doing every 6 months or so to keep perfect.
mine is having some paintwork done at the moment and the garage are going to lacquer mine so I'll see how they turn out.
While I
could apply clear lacquer over a resurfaced lamp, I don't for a number of reasons:
you need to have a finely polished surface for the lamp to work properly. That is the exact opposite of what's needed for the paint to stick.
Clear lacquer also goes yellow over time, and in the sun. That process is sped up with heat, and bulbs get very hot, very quickly.
I don't take the lamp off the car unless it needs other remedial work - like replacing broken adjusters
If you do a good job, which only takes a few minutes per lamp then remember to clean and apply polish occasionally, it lasts for several years
I'm not convinced that most of the yellow surface we buff off is UV damage; it seems more like baked on dirt to me. Often it can be scraped off with a finger nail. Every pair of lamps I've improved has always required more work on the side nearest the kerb, and if you're sad enough look at European cars, this still holds true. And there are lamps that do degrade; look at the top, mostly horizontal edge of a mk1 Focus/Transit Connect/Hyundai Coupe/Vectra/etc and you'll see tiny cracks that go deeper than you can polish out.
So I wont be going to the hassle and expense of painting any lamp. I do wish they still had
glass lenses that didn't suffer from these problems. A good bulb at the centre of a large, round reflector is still very effective