Isobrite is the first T100 watch with 10 year battery life, sapphire crystal, two tritium markers on the unidirectional bezel, 200m water resistant on the market. The "T" rating measures the amount of tritium in a watch. The higher the rating the brighter the watch will be. All other manufacturers have a rating of T25. But as you can see from our description the brightness is not the only unique features of this watch that sets it in a class of its own.