I know there's a couple of threads about headlights and issues with peeling covers etc., but I couldn't find anything about the odd patchy rainbow discolouration I was getting on my HID lights (after-market, upgraded by Tesla). It was annoying; not solved with Windex or any of my normal lights/glass treatments. Anyway, the short version is that I cleaned them by hand using "Meguiar's Sratch-X 2.0" which I routinely use for the clear coat, and they came up beautifully. This product is like an ultra-fine liquid sandpaper, finer than toothpaste. Note that the amount of work is almost zero compared to (e.g.) getting out even a minor scratch with this product. I just dabbed it on and wiped gently a few times, certainly no scrubbing required. So I do not think it is materially reducing the clear coat or whatever coating is on the lights. before (see the patterning/rainbow in the top inner corner of the light): after: So there you go. I'm happy to have found a way to restore the like-new look of those lights. Maybe someone else will benefit from the tip. Ian P.S. Can't get these images to display with the correct rotation. They're iPhone photos and displaying them on the PC works fine but here they are rotated 90 deg left. Sorry about that!