Tell us about yourself!
Since you have a nice setup and I am sure you don't want to damage the light you bought, I think that an easy and inexpensive solution would be to try the lens of a cheap pair of sunglasses (plastic lenses) that provide some UVA/UVB protection. Even if they say 99% that would leave 30mW of your 3W light getting through. If you notice a reduction but the still get a good glow from your protective gear then trim the lens to fit just inside the flashlight for a snug fit. Maybe a drop of PVA or hot glue to hold in place over bumpy sections.
Copper pipe glockenspiel