I was looking at the FAQ to be able to clean my headlights, (because they are really brownish) and I was surprised that it was the outside that was dirty, not the inside. Did I understand well?
yes it's most likely the outside, since thay are plastic, they tend to turn a yellowish colour. Just a few minutes of rubbing with plastic cleaner should clear them up again.
The easiest way to explain why its on the outside is imagine a CD, if you run your Tshirt across it, it could scratch the cd with fine scratches right?
Imagine your headlights and road grime @ 50 mph.
I also updated the FAQ too with some stuff that I have used.