Don't expose the lights to UV light from the sun... It's the plastic, there
isn't much you can do according to people I've talked to in the plastics
industry... why the newer cars don't seem to do it anymore, or not nearly as
badly - better plastics are on the market now.

There are some rub on compounds tho, I use PlastX scratch/swirl remover, but
for your application it's the wrong product.... I use it on the jewel type
headlamp covers on my VW Golf - gets the white off my clear lenses.

use euro glass lenses plastic is a waste of time .