Luminescence in Watchmaking

Why do some watches glow in the dark while others don't?

That was one of the first questions I asked myself when, as an apprentice, I dismantled my first vintage military watch. Inside, I discovered a substance glowing with a greenish hue. Years later, I would come to understand that this glow was more than just a curiosity — it was the result of decades of innovation in luminescence, a fascinating science that continues to light up our wrists after the sun goes down.

In this article, I’ll take you through the origins, evolution, and different types of luminescence used in watchmaking. Get ready to see your watch in a whole new light.

What is luminescence?

Luminescence is the ability of certain materials to emit visible light after absorbing energy. In watchmaking, this technology is primarily used to make hands, markers, or bezels visible in low or no-light conditions. While we take it for granted today, this innovation revolutionized how watches could be used — especially in extreme environments like diving, aviation, or the military.

A brief history: from Radium to Super-LumiNova

The dangerous beginning: Radium

In the 1910s and 1920s, watches began incorporating radium — a radioactive material that glowed continuously without needing prior exposure to light. It was extremely useful... but also highly dangerous. The “Radium Girls,” as the factory workers who painted the dials were called, suffered severe illnesses due to prolonged exposure. Over time, the use of radium was banned in most countries.

Tritium: less risk, same purpose

The next step was tritium — a safer radioactive isotope used from the mid-20th century. While it also decays over time, it was more stable and less harmful. Still, its use today is heavily restricted.

The big leap: Super-LumiNova and beyond

Today, most modern watches use photoluminescent pigments like Super-LumiNova, developed in Switzerland in the 1990s. This compound is non-radioactive, environmentally friendly, and works by absorbing sunlight or artificial light, then glowing in the dark for several hours.

Most common types of Luminescence in watches

1. Super-LumiNova Paint

This is the current standard in mid- to high-end watches. It’s applied as paint on hands, markers, or numerals. The thicker the layer, the brighter and longer-lasting the glow. It’s available in various colors during the day (white, cream, blue, green) and offers strong nighttime glow in green or blue tones. Green is the most common because the human eye perceives it best in the dark.

2. Trigalight (Tritium Tubes)

Some brands, like Luminox or Ball, use sealed tritium microtubes that glow independently for up to 25 years. They don’t need to be charged by light and provide consistent visibility in any condition. They're ideal for tactical or survival use.

These tubes are placed on the hands and hour markers, sometimes even on the bezel for quick-reference timing in dive watches.

3. Electroluminescence (EL Backlight)

Mainly used in digital watches like Casio G-Shocks, this technology lights up the entire screen using an electric current. It’s highly effective in dark environments, though it does rely on the watch’s battery.

Factors that affect glow quality

Not all glows are created equal. The duration and intensity of luminescence depend on several factors:

• Amount of material applied
• Quality of the luminescent compound
• Exposure to a light source (for Super-LumiNova)
• Color of the pigment (some colors glow brighter than others)
• Age of the watch (materials degrade over time)

How can you tell what type of luminescence your watch has?

While many manufacturers list it in their spec sheets, here are some clues based on the glow’s behavior and appearance:

• If the entire screen lights up when you press a button, it’s likely electroluminescent.
• If it glows only after being exposed to light, it’s Super-LumiNova.
• If it glows faintly all the time — even inside a closed drawer — it’s tritium.

Does luminescence have a future?

Absolutely. While it might seem like a small detail, luminescence continues to evolve. New developments include hybrid materials, stronger pigments, and custom solutions for skeleton dials or minimalist designs. It’s also a key aesthetic feature — one that gives brands a unique nighttime identity.

From the dangers of radium to the Swiss innovation of Super-LumiNova, luminescence has marched hand-in-hand with the evolution of watchmaking. Today, it not only improves readability but adds character, heritage, and cutting-edge tech to every timepiece.

Next time you check your watch in the dark, think about everything behind that little glow.