Swiss T100 Tritium Illumination: Isobrite T100 watches have tiny glass tubes that are filled with tritium gas and then hermetically sealed. The electrons of the gas continuously react with phosphorescent paint resulting in a radio luminescent light source that glows constantly for up to 50 years. No external power source or charging-by-light is necessary to maintain the glow. The glow is completely self-powered. T100 means there is up to 100 mCi of tritium gas in the watch whereas the majority of tritium-illuminated watches only have up to 25 mCi. The higher volume of gas results in much brighter visible illumination. T100 represents the latest technology in tritium watches and makes seeing the time in the dark much easier on the eyes. When transitioning from a bright environment to a dark environment, it takes the eyes time to adjust. With the increased visible brightness of T100, the transition is much easier on the eyes.