Should I protect new headlights before they start to turn yellow?

Yes, it can help. New headlight lenses have a factory UV hardcoat, but it slowly wears from sunlight, stone chips and washing, and the lens begins to yellow once it is gone. Keeping new lenses clean and applying a protective coating or film adds an extra layer against UV and grit. Restoration kits are meant for lenses that are already cloudy or yellow; they are not needed on new headlights. Avoid abrasive pads and strong solvents on new lenses.