Lume is the luminous material on a watch’s dial, hands and bezel that makes the time readable in the dark. Modern lume takes in energy from sunlight, lamps or a UV torch and gives it back as a glow. Earlier watches used radium paint, which glowed without light but was radioactive and deadly.
How does lume work?
Modern lume works like a small rechargeable store of light. It takes in energy from sunlight, indoor lamps or a UV torch, then gives it back as a glow. This kind of paint is phosphorescent, and it can go on glowing for hours after it has been exposed to light. It is based on phosphors. One type uses zinc sulfide activated with silver. Another uses strontium aluminate with added dopants. Strontium aluminate pigment can be up to ten times brighter than the zinc sulfide pigments that came before it.
What is Super-LumiNova?
Super-LumiNova is a brand of pigments based on strontium aluminate. They are neither radioactive nor toxic. The Japanese company behind them, Nemoto & Co., was set up by Kenzo Nemoto in 1941 to process luminous paint. In 1998, Nemoto and RC Tritec formed a Swiss joint venture called LumiNova AG. On watches, the pigment lights up the markings on dials, hands and bezels. Hour markers made of steel, gold or other metals can also be filled with it.
How is radioluminescent paint different?
Radioluminescent paint glows on its own, with no outside light, because it contains a small amount of a radioactive isotope. Radium paint was put on watch faces, compasses and aircraft instruments so they could be read in the dark. Radium is radioactive and deadly. From the second half of the 20th century, promethium-147 gradually took its place. The newest radioluminescent materials use tritium, a radioactive form of hydrogen with a half-life of about 12 years.
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