Lume

Lume — short for luminous compound, German Leuchtmasse — is the light-emitting material applied to a watch's dial markers, hands and bezel indices. It allows the dial to be read in low light without an external power source. The technology has gone through five generations; each leaves characteristic traces that are central to authentication and to valuation in the secondary market.

Generations of lume

• Radium (c. 1915 to early 1960s). Self-luminous through the radioactive decay of radium-226, mixed with zinc sulfide that the decay excites. Phased out from the 1960s for safety reasons. Old radium dials are still mildly radioactive and show characteristic burn-out patterns around the lume plots — the phosphor is consumed over decades, the plots no longer glow, but remain as a structural trace.
• Tritium (1960s to late 1990s). Significantly weaker radioactivity than radium, still self-luminous. Ages predictably to creamy yellow, light brown ("custard"), or amber. This patina is the defining vintage look of many Submariner, Daytona and Speedmaster references. Dials of this era carry the marking "T SWISS T", "T < 25" or "T SWISS MADE T" at the lower dial edge.
• Super-LumiNova (late 1990s onward). Strontium aluminate phosphor charged by ambient light. Non-radioactive, so unproblematic in production and service. Available in several colour variants — BGW9 (cool white, blue glow), C3 (greenish, green glow), Vintage Off-White (creamy, yellowish glow). Does not age like tritium; stays bright for decades but lacks the warm patina.
• Chromalight (Rolex proprietary, since 2008). A Super-LumiNova special mix by Rolex that glows blue rather than green — and persists longer (Rolex claims up to eight hours). Standard on modern sports references.
• X1, Grade A type variants. Highest brightness of the modern Super-LumiNova generation; standard on military and professional dive watches.

How lume informs authentication

In the vintage market, lume is one of the central originality markers:

• Tritium and Super-LumiNova do not mix. A 1970s Submariner with brilliantly bright white-glowing lume carries a service dial or fresh plots — original tritium lume should be aged.
• Even ageing. Original tritium plots on dial and hands age in parallel. Visible colour mismatch between index plots and hand fill indicates a part swap — usually hands.
• Lume colour consistency. A uniform creamy tone across all plots is original. Patchy or partial ageing may be damage rather than patina (water ingress, heat, chemical exposure).
• UV reactivity. Modern Super-LumiNova reacts characteristically under UV light. Counterfeit lume often fails to match the OEM phosphor's UV signature.
• Dial designation. "T SWISS T" or "T < 25" at the lower dial edge confirms tritium original. Missing on a 1970s dial means it is not an original dial.

Lume in valuation

For vintage Rolex, Audemars Piguet, Patek Philippe and comparable maisons, original well-aged lume carries a clear premium — typically 20 to 50 percent over an equivalent reference with service dial or replaced plots. For special colourings — "tropical lume" with strongly creamy or brownish patina — premiums can be multiples.

At our atelier in Munich we check lume configuration on every vintage intake under UV light and daylight. Plot colour, plot shape, transition to index edge, and hand ageing are documented; on irregularities we consult comparison material from our reference database.

Service note

At full service the original dial is not touched. A vintage watch returned "refreshed" with new plots has in most cases lost value — the original patina cannot be restored. We recommend on vintage references leaving the dial original even if individual plots are damaged. The decision rests with the owner; we advise on this at our workshop.