You have seen the trick with toothpaste. It works, briefly. The lens comes up noticeably clearer, you feel clever, and within about two months it is yellow again and possibly slightly worse than before.

The reason is the same reason the headlight went cloudy in the first place. A modern lens is polycarbonate with a factory UV coating on the outside. Sun destroys that coating, and once it is gone the plastic underneath oxidises and goes yellow. Toothpaste is a mild abrasive: it sands the oxidised plastic off and leaves you looking at fresh, bare, entirely unprotected polycarbonate. Which begins oxidising immediately.

The distinction that matters in a restoration kit is that it does both halves. It cuts the damaged layer away, and then it puts a sealant back over the bare plastic. The clarity comes from the first step. Whether you still have clarity next spring comes entirely from the second.

That makes the order non-negotiable and the sealant step the one you cannot skip because it is boring. Clean, cut until the haze is gone, dry the lens completely, then seal. Sealing over a damp or dirty lens traps the problem underneath a coat you now have to remove again.

The limit worth knowing before you buy. This fixes surface oxidation. If your lens is hazy on the inside from a failed seal letting moisture in, or if it is crazed with fine cracks all through the plastic, no amount of external work reaches that. Look at the lens under a light. Surface yellow wipes to a clearer patch under a wet thumb. Internal fogging does not change at all.