When most people think of an electrical circuit, they think of a big circle with various components interspersed throughout it. This rudimentary example is called a "series" circuit, where components come one after the other. The electricity travels along the path made by the wires through the components like a train following the rails and stopping at each station. While many electrical devices contain circuits that are wired this way, electrical devices themselves, such as fluorescent lighting tubes, can be wired in the same way, allowing one circuit to run several different fixtures.
Determine the line voltage of the circuit that will carry the electricity to the lighting fixtures. If the voltage is between 105 and 125 volts, as in North America, you will need to use a special dual light ballast. If the circuit is 220 volts, as are most circuits in the United Kingdom and Europe, there is no need for any special equipment.
Connect the first set of fluorescent tubes to the ballast. Do not connect the end pin wire back to the ballast, as you will be connecting the other lamps first.
Wire the pin plates of the first set of bulbs to the second set of bulbs. Attach the wire to the terminal where the ballast would normally be attached.
Run a wire from the end pin of the second set of bulbs back to the ballast. Now the electricity will flow from the ballast through both sets of lights before returning to the ballast, creating a longer circuit that contains two lamps.
Regulate the power flow by installing a capacitor between the end pin of the last lamp and the ballast.
Connect each lamp's glow starter as you normally would, wiring it to both ends of the lighting tubes.
Don't overload the circuit with too many lamps --- two is the maximum number of lamps that can be wired in series before the ballast is overtaxed. Use matching bulbs if possible to make the series run more efficiently. Do not mix bulb standards. If you are using a T8 ballast, use only T8 bulbs in both fixtures.
Never work on any electrical device, including fluorescent lights, without first turning off the power running to the fixture. Failure to do so will result in electrocution, which can lead to serious injury and death. Secure each wire connection with a wire nut to make sure the wires do not come loose or accidentally touch another wire, shorting out the circuit and possibly damaging the lamps.