Glass protects from UV bellow 350nm, which leaves 350nm-400nm band open. So additional coating is required. I might be wrong but such factors as glass thickness and the radiation intensity should be also accounted for. Every physical object is mostly an empty space ...
It actually does not not matter what you see. You can't see UV, and it harms your eyes. What you need is a protection from UV band, and that is exactly what your eye can't see.
