What Makes Watches Glow In The Dark? - Chronoexpert

There’s something magical about things that glow in the dark.  It reminds us of the night sky, of lights glowing through the darkness of a cityscape at night, or of the tiny little glow in the dark stars we stuck to the ceiling as kids.

But it doesn’t stay romantic for very long when you take it down into the detail and start labeling.  Strip away the fantasy and look at how it works, stare at the processes, the labels. But the magic isn’t gone, if you keep going past the terms, then the romance of it all comes back again, once we get behind the science and the bits we understand as humans down to the bits we don’t anymore the magic re-appears again.

That’s what makes this topic so interesting, the combination of romance and science, a mixture of wonder and the technical labels & processes scientists use to explain what is actually going on so we can understand a bit more of how this world works.


What Makes Watches Glow In The Dark

There are two ways light is created, fluorescence and phosphorescence.   Fluorescence is no good for using in anything where you want a long glow because it doesn’t last for very long. The process of phosphorescence takes a lot longer so this is more appropriate for watches, how does it work?  Phosphorescence happens when an electron orbiting an atom absorbs a photon. When this happens it puts it into a higher state and when the electron relaxes light is emitted.

You can tell between fluorescence and phosphorescence because when the light source is removed from the later, you’ll see that it continues to glow for several hours, up to a couple of days.   The glow in the dark stars & paint you used as a kid uses phosphorescence. Fluorescence stops glowing as soon as the light source is removed.

watches for bankers
Credit Rolex.com

Glow In the Dark Method Up to 1960s

Radium paint was used in watchmaking, it began around 1908 and carried on into the 1960s.  So watches made between these dates with glow in the dark functionality may be made with this material. Like most things are initially invented, there is a lot of room for improvement.  There are two major issues with radium paint which meant we had to find an alternative.

Radium Paint Issues

  1. Radium Paint Is Chemically Unstable
  2. It also emits radiation

Radium poses significant health risks & the use of it contaminated 1000 swiss buildings with Radium which now have to be cleaned up so they are safe to work in.  

A quick but important note here, if you own a watch from between 1908 – 1960 and it has glow in the dark features you should check your homes radiation levels with a Geiger Counter.



After Radium we invented different substitutes.  The main ones were Promethium And Tritium & Luminova and Super-Luminova.  The leading luxury watch brands like Rolex, Omega, Breitling, Patek & more use a combination of these depending on the time period the watch was designed.

Rolex, for example, moved from Radium to Tritium post-1960s.  And then they moved to Luminova post-1998.

We’ll provide a brief description of each method of illumination below.



Is a material which still emits radiation but at much lower levels than radium. The issue with this material is that the radiation is lower but so is the glow which can be quite weak.



Tritium is also a low radiation emitter but its half-life is 12.32 compared with Promethium’s 2.62 years.  In normal language that means watch manufactures prefer Tritium for watch-making.


Luminova & Super – Luminova  

These materials do not emit any radiation at all because it works entirely different from the other materials.  Instead of the light being emitted because something is breaking down, in Luminova or Super Luminova light is emitted because it first has been stored.  You can think of it as a kind of light battery. There is no breaking down of materials so it is 100% safe & radiation free. Once it has been charged it can glow for hours afterward.

So, there you go, a quick overview of what makes watches glow in the dark. Science a little bit of magic.

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