Night Fision's Perfect Dot night sights for GlockA(R) pistols offer a revolutionary new design that with brighter, more vivid, aiming dots. Like all night sights, Perfect Dots use self-illuminating Tritium to get the "always on" glow that makes them so effective. The difference is PDs have 30% more Tritium, so they are unusually bright. The Tritium insert isn't surrounded by a painted-on ring, but rather one made of a daylight fluorescing material that produces optimum visibility in daylight. The result is what the Night Fision folks have dubbed the "Perfect Dot". The Perfect Dot provides maximum visibility in both nighttime AND daylight conditions, s Mfg: Night Fision