The tritium sights on my SKS are WELL past their useful lives (based on a 12.32 year half-life for tritium)*.
I can make them glow again for a short period by shining a flashlight on them. This replaces the energy supplied by the radioactive decay of tritium by the energy of the flashlight's photons.
If the rifle has been stored away in the dark (regular room light re-excites them for a short while), you can just barely see them in a very dark room if (A) you know where they are in the dark in the first place, and (B) your eyes are as dark-adapted as your last day in your mother's womb.
Terry
NOTE; REFs:
* This does not mean they just quit after 12.32 years, they're just half as bright as originally. In another 12.32 years, they will be 1/4 as bright as originally. This half-life decay persists until the very last tritium atom in the sight pops its cookies and turns into helium-3, which is not radioactive.
This same process is true of the tritium-powered "EXIT" lights you see all over the place.
(This screams out for a telling of the old joke about "What happens if you start out with an odd number of tritium atoms in the first place?")
Note this
atomic decay half-life is different from the
biological half-life, which is the time it takes for the body to eliminate (pee, sweat, crap, exhale, or metabolize) half of whatever you're talking about. Coffee, for instance, has a
biological half-life of 3 to 7 hours, depending.
And my checking account has an economic half-life of 3.962 days.
https://en.wikipedia.org/wiki/Tritium#Self-powered_lighting
https://en.wikipedia.org/wiki/Tritium