Glow In The Dark Watches
You know how some watches have glow-in-the-dark hands and dials? Until recently, watch companies have been using fluorescent paint mixed with radioactive Tritium. (And before that, Radium, until they found it wasn’t too good for one’s health.) Watches that have tritium in them are marked with two “T”s on the dial. Read about it. Tritium, as a pure beta-emitter does not have very much penetrating power and thus is not a health threat. However, Tritium does have half-life that means its effectiveness in making the paint glow decreases over time. Companies like Omega now use other non-radioactive compounds which do not degrade over time.