There's nothing we like better than clean electricity. Tossing out a set of polluting batteries every week from a bike light is a real downer. A hub dynamo is the most efficient way to generate electricity for your bike light and drag is barely noticeable. The BioLogic™ Joule hub is embedded with a ring of small magnets that automatically generate electricity when the hub is turned while riding. The Joule hub features a polished aluminum hub shell and is made to our 74mm compact width specifications. It is one of the lightest hub dynamos on the market and also one of the most efficient.