Oxidised headlights

One of my own cars has one yellowing headlight, I just repolish it manually whenever I give the car a check over, since it re-yellows in a few months. I use meguires plastrx, usually I follow that with bodyclay, it only takes a couple of minutes total. There is no claimed uv protection in that either and it is hard to see how anything would give a lasting effect, it needs to be in the plastic in the first place. I do know that there was a problem with certain replacement bulbs causing the yellowing on some vehicles (rather than the daylight)