Luminous Watch and Clock

Luminous watch and clock utilize radiation from small amounts of radium-226, tritium or promethium-147 to produce light. Clock hands and graduations are painted with a mixture of radioactive materials and phosphor. The radioactive emissions energize the phosphor which in turn radiates visible light. The radioactivity is only of trace amount and the effect on health is minimal. However, people should avoid wearing watches or placing the clocks nearby the bed while sleeping. Staying too close to luminous watch or clock over a prolonged period will increase the absorbed dose.