The different types of watch lume explained by Extropian

There’s always something fun about a thing that glows in the dark - and watches are no exception! The ‘lume’ that makes them luminous is pretty essential for sports and dive watches - and very useful in all sorts of other situations too! We’re going to have a look at the (slightly scary!) history of lume before explaining the different types that are used today.

A brief history of lume

Lume watches originated in the 1910s and 20s. Back then radium mixed with zinc sulfide was used to produce a bright glow. This material was highly radioactive but no one bothered to tell this to the poor young women who were hired to paint the lume on to watches! Oblivious to the danger they used to wet the brush with the tips of their tongues to keep it sharp. As a result they suffered from a range of hideous health complaints -  anemia, bone fractures, necrosis of the jaw and, eventually, death. Unsurprisingly the use of radium was scaled back and by 1968 it was banned altogether. It was replaced by Tritium, which was significantly less radioactive. This was in use until the 1990s until even safer lumes were discovered. 

Modern lumes

Today there are three types of lume used in watches. They all have their own advantages and disadvantages but we can safely say that none of them will kill you!

Photoluminescence

Pigments based on photoluminescent material (like strontium aluminate) are most commonly used for watch lume today. This type of lume works by absorbing and then re-emitting light. The downside, compared to radioactive materials, is that it doesn't glow so long in the absence of light — it only lasts about seven hours or so in darkness. 

Super-LumiNova

The Swiss brand Super-LumiNova is one of the biggest contemporary suppliers. And their lumes come in a cool range of different shades! Most of the lumes used by the mi-segment brands come here.

• C3 is yellow and has the brightest glow
• C1 is white with about 31% the brightness of C3
• C5 is a greenish yellow with 89% brightness
• C7 is green with 84% brightness
• C9 is a bluish green with around 83% brightness
• BGW9 is a light bluish light with around 95% of the glow of C3

Super-Luminova also comes in a variety of grades - Standard, A and X1. X1 emits the strongest glow but it isn’t available in all shades.

Aerotec - Forte Diver Titanium - BGW9 full lume dial  ❤️ We love the impact of Aerotec’s full lume dial!

Houtman Watches - Murchison - BGW9 & C1 dial mix  ❤️ Wow! The stained glass effect of Houtman’s two tone lume dial is just awesome!

Zelos - Swordfish 40mm SS (Batch 3) - BGW9 ❤️ The Zelos Swordfish certainly comes alive in the dark. We likey!

Nodus - Retrospect III - C3X1 & C1X1 ❤️ We think the minimalist use of lume on the Nodus is oh so cool!

Zelos - Comet 39mm - Black SuperLuminova ❤️ The subtle effect of Black lume on the Zelos Comet is super sophisticated!

Zelos - Swordfish 40mm SS (Batch 3) - Light Orange Lume ❤️ Switches from orange in daylight to yellow and blue in the dark! How cool is that?

Gruppo Gamma - Peacemaker - Old Radium (Vintage style lume) ❤️ Want the best darkness visibility there is? The Swiss Super-LumiNova on this Gruppo Gamma Peacemaker will give it to you!

Circula - Aquasport II - C3X1 & BGW9 ❤️ Blue and green is definitely something to be seen on the Circula Aquasport II!

Seiko’s LumiBrite

Seiko have their own version of lume which they call LumiBrite. It only takes ten minutes of exposure to natural light or artificial light stronger than 500lux for it to glow at full brightness. And the light will last for a pretty impressive 3-5 hours. 

Tritium gas tubes

A few watchmakers are using Tritium again - but not as a paint. Instead Tritium in gas form is placed in borosilicate glass tubes that have been internally coated with a phosphor layer. The tritium gas undergoes beta decay, which releases electrons, causing the phosphor to glow. It is still radioactive but, don’t worry, the gas poses little-to-no risk in the tiny amounts found in Tritium tubes!

The benefit of Tritium gas tubes is that they don’t fade after a few hours. The downside is that the material only has a certain active life span. After 12 years it will only be half as radioactive and eventually the tubes will need replacing. 

Electroluminescence 

Electroluminescence gets its glow as a result of an electrical current passing through a phosphor. A glass or plastic panel is coated with an electric conductor and a phosphor and this is then mounted behind the dial. By pressing a button an electric current is delivered, which causes the phosphor to react and act as a backlight.

You’ll mostly find this kind of lume in battery powered digital watches, but a few producers do use it in analog watches. 

Conclusion

So, yes, glow in the dark watches have a slightly scary backstory but these days there is nothing to worry about!