The Trijicon ACOG TA31F Rifle Scope features Dual Illumination (Fiber Optic system provides daylight illumination and tritium illuminates reticle at night). The ranging reticle is calibrated for 5.56mm rifles out to 800 meters. ACOG(Advanced Combat Optical Gunsight) rifle scopes are internally-adjustable, compact telescopic sights with tritium illuminated reticle patterns for use in low light or at night. Bindon Aiming Concept (BAC)* models feature bright daytime reticles using fiber optics which collect ambient light. *The TA31F 4x32 model uses the Red Chevron reticle and includes the TA51 flat top adapter Trijicon ACOG TA31F rifle scopes combine traditional, precise distance marksmanship with close-in aiming speed. Although the Trijicon TA31F ACOG rifle scopes have many features which are very advantageous for military use, they were developed by Trijicon without government funding. Designed for use with the M16 family, every feature of its mechanical and optical design was chosen for a single purpose: to provide increased hit potential in all lighting conditions -- without failure-prone batteries.