Dynamo Lights

There are two main types of dynamos for bicycles; The first, the bottle dynamo, is known in the US as a sidewall dynamo, and is effectively a small generator which runs off the tyre or occasionally the rim to power the lighting system. Named after their resemblance to bottles they work by using a roller at the top (like the lid of the bottle) which is spun by the turning wheel by placing it against it. Traditionally, if the bicycle stopped then the dynamo ceased to provide power to the lights, but newer versions have 'stand lights' which stay on for a few minutes. Unlike the older hub dynamos* which work inside the hub of the wheel and which provide a smaller level of constant resistance, the bottle dynamo can be withdrawn from the wheel when not in use and therefore have no resistance. They are also generally cheaper than hub dynamos and can be easily retrofitted to a bicycle. * It's worth noting that newer hub dynamos do not create any resistance when they are 'off' so whilst they are much more expensive, they are also far more efficient.