Boaz sells sheets of “DC Fix” which does exactly as in the pic, as it’s frosted to grainy, with adhesive or without.
For small lights, or in general, lights that are not to be used as throwers, it’s quite handy, and gives a nice diffuse beam like a TIR lens… sort of.
For smaller lights (eg, those which use AAs/14500s/16340s), it’s quite handy and makes a very useful beam for looking close-in.
Also, if you put the adhesive-backed film on the outside of the lens, it can be removed and replaced as needed, well, as long as the adhesive doesn’t get dirty and later refuses to stick.
’Though for me, for smaller lights, I’d much rather TIR lenses AND NO GLUE, so that the lenses can be swapped, as TIRs come in everything from 5° to 90°. I’ve gotten the best and most useful beam with a 60° TIR lens in a 4C S2+. Beautiful “warm sunlight” beam, no fried-egg look (yellow hotspot, blue-white spill) as with the reflector.
I have 3 different-model LuxPro lights which use G3s as the emitters, and they have horrible, horrible, beams. Neutral hotspot, blue-white spill, and a strong urine-yellow corona around the hotspot. Hideous. :confounded: DC Fix in fact fixed that right up, but a TIR lens would do the same, had they used them instead of reflectors.
I keep harping on mfrs offering TIR lenses (yeah, yeah, AND NO GLUE), so that the beam can be changed at will by taking 5min and swapping out one TIR for another.
One last example, my Boruit RJ02 headlamp has a simple screw-on bezel holding in the TIR lens, and I can go from 5° to my favorite 60° in under a minute, no tools needed.