Tritium Use

This page describes the basic use of tritium by Rolex in their timepieces.


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"Tritium illumination is the use of gaseous tritium, a radioactive isotope of hydrogen, to create visible light. Tritium emits electrons through beta decay, and when they interact with a phosphor material, fluorescent light is created, a process called radioluminescence. As tritium illumination requires no electrical energy, it found wide use in applications such as emergency exit signs and illumination of wristwatches. More recently, many applications using radioactive materials have been replaced with photoluminescent materials." source:

In order to read a watch in the dark, a luminescent material must be applied to the hand and hour markers of the watch. The emission from a watch is caused by one of two types of luminescent material; photo and radio. Photo luminescence is determined by an exciting luminous radiation. Radio luminescence is determined by the radioactivity of the material.

Rolex used the chemical Tritium from the 1950’s until the late 1990’s to illuminate their watches. To indicate the amount of radioactive material in the watch, Rolex began placing a mark at the bottom of their dials:

  • T SWISS MADE T: T Swiss Made TThere is Tritium on the watch. The maximum amount of radioactive material emitted from the watch cannot exceed 25 milliCurie.

  • SWISS T < 25: Swiss T<25The amount of Tritium emitted from the watch is less than the 25 milliCurie limit.




  • SWISS T 25: The amount of Tritium emitted from the watch is a full 25 milliCurie, or the maximum allowance.

  • Swiss MadeSWISS or SWISS MADE: This indicates the presence of the luminous material LumiNova on watches produced circa 1998. Watches produces in the 1950’s carry this indication as well but would indicate nothing more than that the watch was made in Switzerland.




  • T: Deposits activated by Tritium.
  • Pm: Deposits activated by Promethium.
  • T 25: Deposits activated by Tritium on higher value watches.
  • Pm 0,5: Deposits activated by Promethium on higher value watches.

Rolex timepieces featuring radio luminescence are mainly designed for specific use and include models like the GMT-Master I & II aviation watches, and the Submariner diving watches. The ISO 3157 Standard has strict guidelines when using radioactive material. This standard allows only low values of two types of radionuclides: Tritium (3H) and Promethium (147 Pm). These materials emit a radiation of low energy. Rolex watches that use Tritium with their luminescent parts are not harmful when sealed inside the watch.


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