The bicycle reflector or prism reflector is a common safety device found on the rear, front and wheels of bicycles. It uses the principle of retroreflection to alert another road user of the bicycle's presence on the road.
The reflector is usually manufactured in the form of a moulded tile of transparent plastic. The outside surface is smooth, allowing light, such as from a car's headlights, to enter. The rear surface of the tile takes the form of an array of angled micro-prisms or spherical beads.
The light striking the rear, inside surface of the prisms or beads, does so at an angle greater than the critical angle thus it undergoes total internal reflection. Due to the orientation of the other inside surfaces, any light internally reflecting is directed back out the front of the reflector in the direction it came from. This alerts the person close to the light source, e.g. the driver of the vehicle, to the presence of the cyclist.
- Complete physics, Stephen Pople 1999