This is a Truglo Sight known as the Brite-Site, model TG131GT1.
Truglo Glock Low Set (Green/Green)- When you need to make a fast and accurate shot" brightness counts. They brought fiber-optics to the shooting sports industry years ago for this very reason. They have now paired them with their tritium night sights to create a consistently bright sight picture-day or night! Their patented combination of Tritium and Fiber-optic technologies unites the best of both worlds. Whether you are in glaring daylight or complete darkness" you can count on TFO(R) to provide a bright and reliable sight picture.
Features:
The Ultimate handgun sight
Glows in the dark
Fits standard holsters
Tritium/fiber optic
Green front and rear