(Pic is taken from Wikipedia.)
My tritium powered Nite glowring just arrived. It’s green and I really like it! The one on the pic above glows a bit stronger than mine, but I think that’s caused by the camera. (Probably made with an extra long exposure time) The package says it’ll glow for at least 10 years and since the half-life of tritium is around 12.32 years, it actually sounds plausible. Naturally there are only around 3,5 kilograms of tritium on our whole planet so mine is probably waste from a nuclear power plant.