A high level of readability is crucial when developing a mechanical watch made for dark and muddy waters. A common solution is to use various luminous materials printed or glued on the watch dial and watch hands. Luminous materials comes in a many different shapes, colors and nuances and performs on various levels in strength, glow effect and durability. Common for all lume is that it needs to be charged with a light source. For some a flash of sun- or daylight is enough and for others a close and strong light source, like a flashlight, is required to activate the luminous effect. 

An alternative to traditional lume are so called tritium tubes. Tritium is a radioactive isotope of hydrogen (hydrogen with two extra neutrons) and is well known in the world of watches for its ability to glow in the dark on its own without any light source. This is beneficial for divers because flashlights and other strong sources of lights can easily damage their natural night vision and greatly impair their visibility for the rest of the dive.

Tritium is, most often, produced by man and exists in a relatively instable form of gas that continuously strives to reach a more stable form, in this case an isotope of helium. It’s the process of decay from hydrogen to helium that generates the energy used to create luminous effects. 

Tritium used in watches and watch dials are capsuled in small tubes sealed in glass. On the inside of the glass there’s a surface of phosphorescent paint that can absorb the energy emitted by tritium and release the energy as a luminous effect. Phosphorescent paint comes in many options, therefore it’s possible to choose the color of its glow. There’s also different qualities avaliable when using tritium tubes where higher quality often suggests that each glass tube contain a larger amount of tritium. Since its not possible to see the actual decay of tritium by eye, the quality of the phosphorescent paint is important in order to capture the larger amount of tritium and translate it into glowing colors. In that way, the amount of tritium and the quality of the paint are both of great importance when trying to create a strong luminous effects.

The tritium tube’s ability to glow by its own makes them very popular and usable in dive watches. Important to note is that the capacity and effect of the lume is decreasing after time, and after around 5-8 years the decrease is noticeable. You don’t replace the tritium tubes or “recharge” them in any way. Instead, the whole dial is needed to be replaced with a new one. All handling of tritium, from manufacturing, assembly, maintenance, stock and sale, requires a special permission provided by the Swedish Radiation Safety Authority and all tritium must be handled with care by an approved radiation safety function.