Watch Lume Explained: Tritium, Super-LumiNova and Seeing in the Dark

Lume is the glowing material on hands and markers that lets you read a watch in the dark. It started as a safety feature for pilots, divers and soldiers, and it remains one of the most practical details on a tool watch.

Early luminous watches used radium paint. It glowed continuously because it was radioactive, which later proved dangerous to the workers who painted the dials. Radium was phased out in the middle of the twentieth century, and vintage watches with original radium lume should be handled and stored with care.

Tritium replaced radium. It is a weakly radioactive gas sealed in tiny tubes or applied as paint, and it glows by itself without needing light, but its brightness fades with a half-life of around twelve years. Some brands still use tritium tubes on military-style watches because they glow all night without charging.

Today most watches use photoluminescent pigments such as Super-LumiNova. These are not radioactive. They absorb light, then release it slowly as a glow. A short exposure to daylight or a torch charges them, and the glow is bright at first, then fades over several hours. Different colours, such as blue and green, glow differently, and thicker application glows brighter and longer.

When judging lume, look at how evenly it is applied, how well it contrasts with the dial in daylight, and whether the hands and markers glow the same colour. A watch with excellent lume is a real pleasure to use, especially a diver, and it is worth checking photographs or reviews of the glow before you buy.