On headlights with removable bulbs, I have had good success removing the headlight from the vehicle, removing the bulb, pouring a little 70% (or 90% if I have any on hand) rubbing alcohol into the light housing, swirling it around with the lens pointed downward, empty, repeat, let dry (with the lens pointed upward), reassemble. The alcohol may leave some spots on the inside of the lens, but not enough to pose a problem or be noticeable (to me at least).