Do not put anything (or alter in any way) the sides of an optic. Let me say that again: Do not put anything (or alter in any way) the sides of an optic.
Optics work by internal reflection. If you coat the outside (or try to modify it in any way), you ruin the optical properties. What you can do is add glow-stuff to the base of the Lux, on the emitter board, or inside the bezel. That'll give you an eerie glow if you use an optic.
For outside of flashlights, you can mix clear epoxy with GID powder and put that on any grooves you may want.
The search function will be running again shortly. When that happens, search among Darkzero's old threads. I'll say this again, he's the master of GID+epoxy application and he's posted his secret methods for us to use :nana:
My cousing greenligh has also done some pretty cool things with glow-stuff.