Some years ago, a friend convinced me I needed an Inova X1 LED flashlight. He was right; I’ve carried one in my belt pack ever since and, in fact, added a couple of X5s to the household armory.
Perforce, this is an old X1 with a coated glass lens to make the best of the LED. Newer X1s don’t have (or, likely) need the lens, as LED technology has made great strides in the last few years.
I couldn’t bear the thought of that lens rattling around in my belt pack, chewed upon by the assortment of other crap in there. So I made a lens protector: a length of heatshrink tubing with a polypropylene window. You might want to do the same for your flashlight to keep from grinding up the optical surfaces on its shiny end.
This tubing has an internal thermoplastic glue, but ordinary tubing would likely work as well. Position the tubing over the end of the flashlight with a few millimeters sticking out. Cut a circle from the clamshell case around some piece of consumer electronics, drop it on top of the lens, and shrink the tubing around the flashlight: watch it wrap right over the end and hold the circle in place. A dot or three of urethane glue may help for glue-less tubing.
It’s transparent enough for most purposes, but when you really need more light or a tighter beam, pull it off. That’s aided by dabbing a trace of oil on the X1, which you can get directly from the (outside) of your nose. Yeah, gross, but it’s a renewable natural resource…