Tritium Light

What is the Tritium lighting?

Tritium provides a constant light source that requires no additional power source. There are no buttons to press. The tritium is active every day for up to 25 years. Simply looking at the watch tells you exactly what time it is. Tritium ensures easy reading; the light is perfectly visible even in complete darkness. No other lighting system can boast these advantages. Today, after all these years, many museum watches that used this technology no longer show signs of tritium atom decay. 

Here's a module 1015471_E that was used in wristwatches.