If you own a Chrony, you need these lights for days when you can"t be outside to chronograph your guns.•The lights attach to the skyscreens of any Shooting Chrony so you can measure velocities indoors. You MUST use them in a room that has no fluorescent lighting. They"re sufficient to operate the skyscreens by themselves, and no other lights are required.• Lights plug into 120-volt house current & come with 6-ft. cables, diffusers and wire rods.