Nite Ize See'Em Mini LED Spoke Lights are tiny lights that clip onto bicycle spokes to make your wheels visible from the side at night. Each pack contains two See'Em lights with green LEDs. Twist the light to switch it on or off; it glows steadily and runs for about 24 hours on its replaceable 927 3V lithium battery, which is included. They are weather-resistant and easy to attach and remove on the most common spoke types: oval, round and bladed (flat). Each light measures about 25 x 25 x 21 mm and weighs only 4 g, so it does not unbalance the wheel. Not for use on carbon spokes. Fit one per wheel or both on the same wheel for more light.