Two fluid arcs of light are formed by LEDs programmed to detect your speed and illuminate when oriented at the front or rear of the bicycle. Revolights cast 360 degrees of illumination, making it much easier for others to see the rider. This improves safety tremendously - most nighttime bike-car collisions are due to inadequate side visibility. Revolights also throw a uniquely even and wide vertical swath of light, illuminating not only the ground but road signs and elevated obstacles as well. They are resilient and easy to mount on the wheels of the bike.