Iron sights into which glass capsules coated with a phosphor and containing the radioactive gas tritium have been inserted. As the tritium emits electrons, the phosphor produces visible light, perceived as a glow, useful for sighting at night or in low-light conditions. Green is the color of the phosphor most commonly used, although in some designs the front sight is given a different color than the rear sights to allow a shooter to distinguish between front and rear sights and thus aim more easily. Also called self-luminous iron sights.
1