That's a green "navigation light", a low-profile supplement to the main spot or flood light. Navigation lights are red, green, or orange, and are intended for immediate-area illumination (hopefully, without tipping off the enemy!).
To be real sneaky, use infrared lamps and glasses.
Some green targeting lasers are making an appearance, but I haven't seen one for a pistol yet.
Green would be superior for daylight use.
But you reach a point of diminishing returns... Anybody see the Alien Vs. Predator movie, where the visible beams of the green lasers, on the assault rifles, did a spectacular job of leading the bad guys to the shooters?
Dumb! :freak: :crazy: :uglylol:
--Ray