Riding your bike doesn't have to stop when the sun goes down - get a light! There are a lot of great lights for sale, but some prefer to build their own light*system. Although building your own won't necessarily save you money, there is a sense of pride and satisfaction that comes from building your own light system. Before you can start building your own light, you need to understand the different parts of a light system. A light system can be broken down to: light source, optics, power source and housing.