You will occasionally see tritium in a watch but more often a luminescent paint is used. It has to be "charged" by direct light for it to glow and except for the really high end stuff (Omega, Rolex) doesn't last super long. Tritium simply glows all by itself ,from my understanding, and is in a liquid form. You get it to stay I one spot by trapping it in some kind of container. Take a look at night sites from trijicon or meprolite for a good example.