This is an accessory Green Lens for the MF Tactical Sierra-P flashlight. This color filter lens easily replaces the standard clear lens. Just unscrew the flashlight bezel, remove the clear lens, replace with the color lens and replace bezel. This lens is made of hardened mineral glass, which is resistant to scratching or breakage. It will also outlive and outperform similar products made of plastic.
A green filter is used when you need more light, but you don’t want others seeing you easily. Green light diffuses much more quickly than do other colors, so your beam is not as easy to see from a distance.