Tritium is a type of luminous paint used to illuminate the hands and markings of watches and other instruments. It is a radioactive isotope of hydrogen and emits a low level of radiation. It is non-toxic and safe to use, and its light is created by a chemical reaction between the tritium and oxygen in the atmosphere rather than electricity. The light it produces is a soft, greenish-blue glow that can be seen in the dark. It is often used to allow for easier time-telling in low light conditions, and its long-lasting qualities make it a popular choice among watchmakers.
