Lamps connected in series. Animation showing a simple circuit (one lamp) and two lamps connected in series. The potential difference (voltage) of the battery (left) causes electric current to flow round the circuit, which lights the lamps. The arrangement of the circuit affects the brightness of the lamps. When they are connected in series (as here), the battery is working against a greater resistance than when the lamps are connected in parallel, and the battery drives a smaller amount of current through the lamps. When connected in parallel to the same battery, the lamps will be brighter.