Isobrite is the first T100 lightweight polycarbon watch with 10 year battery life, sapphire crystal, two tritium markers on the unidirectional bezel, 200m water resistant watch 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 of polycarbon cases have a rating of T25. The brightness is not the only unique features of this watch that sets it in a class of its own. Please check out the features and you will find this the best lightweight polycarbon watch available period.