It was determined that light bulbs in a series circuit is dimmer while light bulbs in a parallel circuit is brighter. I know this because in a series circuit it’s basically a voltage divider, in a parallel circuit, it doesn’t do that. Two bulbs in a parallel circuit each enjoy the full voltage of the battery. This is why the bulbs in the parallel circuit will be brighter than those in the series circuit. While the series circuit is dim because when your pushing current through multiple light bulbs it causes voltage drops. With the current leaving behind energy after every light bulb, the lamps glow dimly because of voltage drops.