The Mepro M21 is a maintenance-free, self illuminated, red dot reflex sight especially designed for quick and instinctive accurate shooting. Illumination of the point of aim reticle is achieved by a fiber optic collector system during the day and by a miniature self-powered tritium light source at night. Features a large 30mm display window that allows the shooter to keep both eyes open for better battlefield situational awareness; large field of view; optimized eye relief; withstands heavy recoils and rapid target acquisition.