A 6-V battery powers a circuit with parallel branches on a board. Several wires and light bulbs plug into the board to make various series and parallel circuits. The brightness of the bulbs changes ...

or parallel to, each other. This simple circuit is like a one-bulb version of a building’s lighting circuit. In a parallel circuit, if you want to add more bulbs, you add them on their own ...

Some of these could be replaced with a working bulb, but not all. The other type of circuit light strands use is a parallel circuit. In this setup, each bulb is on its own circuit to the power source.