Really "shines" when other sights are useless. No switch to turn on, no batteries to wear out. Both front and rear blades have their own green tritium gas light source and provide a green/green , 3-dot sight picture. The front sight is always green for contrast with the rear sight. Unaffected by weather, gun solvents or oils. Used by NATO, U.S., and Israeli armies. Also ideal for law enforcement and others requiring accuracy in low-light conditions. Contains both front and rear sights. Rear sights either replace the original rear entirely or, as on S&W revolvers, a new rear leaf, screw and nut are provided. Front sights either replace the original (1911 Auto); slip over and Mfg: Meprolight