Lume refers to the luminescent material applied to the hands, indices, and sometimes other parts of a watch dial to enhance visibility in low-light conditions. In watchmaking, two primary types of lume are commonly used: Super-LumiNova and Tritium.

Super-LumiNova is a non-radioactive, photoluminescent pigment that charges when exposed to light and emits a glow in the dark. It is made from strontium aluminate and is known for its bright and long-lasting luminescence. Super-LumiNova is widely used in modern watches due to its safety and effectiveness, providing a bright glow that can last for several hours after exposure to light.

Tritium, on the other hand, is a radioactive isotope of hydrogen used in self-luminous watches. It is encapsulated in tiny glass tubes coated with a phosphorescent material. The beta radiation emitted by tritium excites the phosphor, causing it to glow continuously without the need for external light exposure. Tritium lume is valued for its consistent glow over many years, typically lasting up to 25 years, but it is less bright compared to freshly charged Super-LumiNova.

Both Super-LumiNova and Tritium play crucial roles in enhancing the functionality and aesthetic appeal of watches, allowing for easy readability in darkness and contributing to the overall design and allure of timepieces.