The O2 BEAM was developed specifically for long distance lighting and this model features a green light. Green light is best for low light conditions, because the human eye recognizes the color green faster than other colors. Also perfect for hunting, as some game cannot see green light. The mount with this light fits (20mm - 32.5mm) barrel and scope diameters, and adjusts, tighten, and locks without tools. This light has an output up to 400 lumens.