Plenty of people use night sights, and they are required equipment in most law enforcement and military pistol procurements these days. But how, exactly, do those glowing sights work?
In a tritium night sight (such as the ones made by Trijicon), a glass tube is coated with a phosphorescent material and filled with a tiny amount of tritium. Tritium is a radioactive isotope of hydrogen, with a nucleus containing two neutrons (whereas a “normal” hydrogen atom’s nucleus has no neutrons). As the tritium decays, it releases electrons and their energy excites the tube’s coating, causing it to fluoresce.
Because the decaying tritium provides the energy to fluoresce the phosphorescent coating, no outside light source is required. This means that even if you left your pistol in the dark for an entire year, the sights would still glow just as brightly as if you’d left the gun in the sun every day. That is the main advantage of tritium sights: they are visible under low-light conditions at a moment’s notice.
While the tritium gas is radioactive, there is a ridiculously tiny amount in the glass tube of a night sight. One report estimated that the entire world-wide commercial use of tritium amounts to less than one pound per year. That includes not only night sights but watch dials, compasses, and emergency exit signs … all of which commonly rely on GTLS (gaseous tritium light sources). Also, the relatively weak emissions of tritium gas cannot penetrate glass or human skin. Only by inhaling or ingesting the gas could it cause any harm, and the volume of gas in a typical set of night sights is so miniscule as to be meaningless in terms of a health risk.
Contrary to common belief, the green color is not from the tritium itself. The color of the sight is determined solely by the phosphorescent material coating the glass tube. So it’s relatively easy for a manufacturer to choose green, red, yellow, orange, blue, or even purple. The most common color for night sights is green, because the eye can pick up that color the easiest.
Tritium has a half-life of just over twelve years. This means that half the gas in your sights will have decayed in twelve years, giving off effectively less light. For this reason, most night sight manufacturers warrant their sights to be visible in dark conditions for ten to fifteen years.
Train hard & stay safe! ToddG
my fiber optic sight hasn’t worked in low light from day 1. does this mean the tritium is all worn out inside?
Fiber optic sights and tritium sights are two different things.
There is one company making a tritium-powered FO (“TFO”) sight, but after using it for a while on one of my pistols I decided to go back to normal tritium sights. The TFO was very wide and the fiber optic tube became dim from wear very quickly. Unlike normal fiber optic sights, the TFO does not have user-replaceable fiber optic tubes.