Why Does A Watch Light Up In The Dark? – A Guide To Luminous Watches

You’ve probably seen at least one watch in your lifetime where the dial was giving light in the dark.

There is no actual light bulb inside of it, but how does that watch give light? It’s called watch illumination and I am gonna guide you through it in this post.

What Is A Luminous Watch?

The definition of “Wacht Luminous” is a watch that glows in the dark.

That way you can tell the time even in the darkest of places when there is no light near you.

Considering that not everyone likes to wear a digital or smartwatch this is a must-have for a lot of watch owners.

So having your hour and minute hands glow up in the dark makes telling time in the dark a piece of cake.

Some watchmakers even make the hour markers luminous so you don’t have to hesitate about the time.

There are even watches that give a whole luminous dial so you can tell the whole timepiece without a chunk of light.

An Omega Speedmaster Reduced in different light surroundings

How Does A Luminous Watch Work?

Everyone knows what luminous watches are but a few really understand how they work.

To answer that question we have to explain some chemistry.

Objects can glow in the dark using a powder called phosphorescence.

When exposed to light a phosphorescent object will glow, absorbing the light and energy it reemits for some time.

Using this saved energy the watch can shine in the dark so you can tell the time.

Materials on watches are given a photoluminescent coating.

Photons get absorbed from light and the phosphorescent material will slowly release the light back out.

This process takes some time, hours may go by until all the energy from the phosphorescent material is released.

That way a watch can shine all night.

The Consequences Of Luminous Watches

Just like a light bulb, a phosphorescent watch won’t last you forever.

Eventually, the material will stop shining.

It gives you the choice to replace the phosphorescent parts or get a whole new watch which can shine you through the night.

When replacing the parts you need to consider if you want to keep the watch as original as possible or do you want to tell the time when it’s dark.

The moment you replace parts of your watch it is possible that the value will drop.

Keep that in mind if you would like to resell your watch one day.

At this age, I can assure you that wearing a luminous watch is safe.

But this hasn’t always been the case.

At the beginning of the 20th century when luminous watches were introduced they used a radium coating to make the parts shine.

Radium is a radioactive material and can cause damage to the human body when coming into contact with it without wearing the proper protection.

The pro of radium was that it didn’t need a light source to get energy from.

Radium would glow out of itself.

Unlike phosphorescent coated watches, radium covered watches needed a new layer of coating every couple of years.

Tho they wouldn’t glow up anymore after those years the parts that were covered in radium would still be radioactive.

To this day there are watches with these original parts.

Don’t worry they won’t turn you into Superman.

Phosphorescent bird figure

Development Of Luminous Watches

Watchmakers soon realised that making luminous watches out of radium was not their best idea.

They started searching for alternative materials which would make the watches shine without doing any harm to the people that wore them.

They came across tritium, which had lower levels of radiation and longer life than radium.

Promethium was also a possible alternative but it did not have as much glow as the radium covered watches.

Tritium paint was the go-to for watchmakers.

With the slower rate of losing the glow, it was more efficient than radium and it had a good amount of glow.

Tho the alternative to radium was good the search for something that could be safer continued.

That’s where Luminova and Super-Luminova came.

The phosphorescent substance is not radioactive or toxic in any way.

It gives a great amount of glow to watches. This is the go-to nowadays for watchmakers.

Super-Luminova Glow In The Dark

Luminous Watches Now

When the time passed by it got cheaper to produce phosphorescence so a lot of watches glow up in the dark nowadays.

It doesn’t harm the human body in any way thus making it safe to wear.

Tho more watchmakers make glow in the dark watches we still can see that the more premium watchmakers’ products often glow way more in the dark.

They use more phosphorescent paint, which explains that.

Right now watchmakers make the step to switch to Super-Luminova.

A substance created in Japan which has zero radioactivity and shines for hours in the dark.


The guy who loves to chat about watches.

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