The Lumenok lights up instantly with shot inertia and stays lit, so you can track your arrow to your target and find it easily after dark. Glows for up to 40 hours until switched off. Replaces existing arrow nock, adding only 22 grains to most popular carbon arrows and aluminums with the Super Uni-Bushing system or Gold Tip, and only 16 grains to ST Axis, Beman MFX and AC Super Slim arrows. Available: Single-pack, Three-pack. Colors: Fluorescent Red, Fluorescent Green, Pink.