I am forever misplacing my kleys or having trouble locating them in the dark so I recently ordered one of those inexpensive Tritium key chain lights. I received it today. It glows a yellow/green colour. I chose green because it's the most visible colour. It's not very bright but it's fine under dark or semi dark conditions. Not quite as bright as the old radium lights but still good enough for practical use. It's basically a laser sealed phosphor coated glass tube containing a minuscule amount of radioactive tritium hermetically sealed in a clear polycarbonate enclosure. Tritium has a half life of 12.6 years so, in 10-12 years it will probably be only about half as bright as it is now. I held it up to a Geiger counter and there was hardly any increase in counts per minute. Contrast that with one of my old radium dial pocket watches that make the Geiger counter click away like crazy if I bring it close to the tube. Radium has a half-life of >1000 years so watches painted with radium are still quite as radioactive as when they were made decades ago. The only reason they no longer glow is because over 10-12 years the phosphor goes bad. Although they don't last as long the tritium lights are considerably safer.