As I understand it, this sight has both a Tritium part that is the "night sight" part of the sight as well as a fiber optic rod that gathers sunlight or other light for brightness during the day. The Tritium has a half life of around 12 years, so be careful on manufacture date when you purchase, especially through eBay and Amazon. If your sights are that old or older that may well be why they no longer glow as bright at night.