Are there radioactive substances in watches?

Once upon a time all luminous watches used to contain dangerous radioactive substances. At a time when Marie Curie herself held a tiny vial of Radium on her bedside table. She watched it glow in the dark

marie and pierre curie radium

Until the 1960s, phosphorescent paints containing Radium (Ra-226) or Promethium (Pm-147) were commonly used by watch makers to light up the dials of their products. During the First World War soldiers could upgrade their pocket watch or wristwatch by applying on few dots of radium paint on the dial, next to the hour numerals. They could also replace the hands of their watch with radium-coated hands. These early radioactive substances were replaced by Tritium well until the mid-90s.

Tritium is still present today in some watches, but only in gas form in tiny narrow glass tubes coated with a phosphorescent color. The tritium radiation stimulates the luminous coating to produce visible light, which makes these watches glow in the dark.

Why do watch manufacturers still use radioactive substances?

Traditional phosphorescent paint needs to charged with ambient light for a few hours to glow in the dark. If the owner doesn’t take the precaution of exposing his watch to a source of light before going out at night, he might not be able to read the time on his device when darkness falls.

A tiny quantity of a radioactive substance is able to constantly stimulate the phosphors contained in radioluminescent reactive coatings to generate a visible glow at all times.

That’s why high end watch manufacturers still use a tiny dose of radioactive substances in some of their models (they have to label them H3, T or T25 on the dial).

Is it dangerous to use radioactive substances in watches?

The quantity of radioactive compounds still used today in gas form in some high end watches is very limited and totally inoffensive for the consumer.

Is there an alternative to luminous watches to read the time in the hours of darkness?


Yes, it’s a pocket device 30,000+ times more powerful than the best Apollo era computers. We call it a smartphone, available both to iOS and Android users.

You can even use an old-style feature phone or a cutting edge Apple Watch or one of its Android siblings. They’re cheap and look almost like their inspiration from Cupertino.

Do these marvels of Chinese technology contain radioactive substances? That could be the topic of another article…

android smartwatch glow in the dark

Logo