How Do Bike Lights Work?

Many bicyclists choose a dynamo to power the light on their bike, states Gizmag. These small generators require no batteries and create electricity by turning a permanent magnet through a coil of wires.

Bottle dynamos have a long history of powering bicycle lights. These small devices mount next to the tire. A small gear uses friction to turn the magnet inside the bottle that also contains the wire coils. Dynamos provide about 3 watts of electricity when the bicycle wheel is turning. This is enough power to light a small incandescent or LED lamp.

Bottle dynamos cause unnecessary wear on the tire sidewall and slow the speed of the bike when lighting the path. As a result, many bike riders prefer hub dynamos, built into the hub of the bike, even though they add revolving weight, according to Gizmag. When the bicycle speed slows beyond the minimum, the lamp goes dark when using a dynamo-powered light. This leaves riders less visible to traffic and makes it more difficult for them to see. Bottle dynamos also tend to slip if the tire is wet or spins too quickly, so they become less effective at producing light. Some manufacturers include capacitors to store energy, providing light for approximately five minutes, even if the dynamo is not turning.