Bicycle dynamos are small generators that supply your bike lights with electricity while cycling – this means that the lights are only on while riding. Not all dynamos are equally effective. You should therefore pay attention to good low speed power and a built-in ball bearing. The German Road Traffic Licensing Regulations stipulate a maximum voltage of 6 V and a maximum power of 3 W. There are different types of dynamos, such as hub dynamos and sidewall dynamos.