Many watches use tritium to illuminate watch hands and markers, making them visible in the dark. Tritium is a radioactive isotope, so there have been some concerns as to its safety. Indeed, watchmakers working with the material are required to do so with special workbenches that are equipped with a vacuum hood to remove small radioactive particles and harmful vapors. Once they are placed inside the watch, however, they pose no further threat to either the assembler or the wearer.
Despite studies that show that radiation exposure from a watch with tritium is negligible, fear from potential buyers has led some watchmakers to introduce new materials, such as LumiNova and LumiBrite, without radioactive isotopes. While meeting minimum standards for visibility, these materials do not last as long as tritium and also require longer charging periods.