A 40 watt fluorescent tube lamp or two 20-watt tubes in series will be driven by this circuit but this circuit will produce less brightness than usual, since this circuit only deliver 6-12 Watts. This circuit draws 0.9-1.2 Amps for 2 x 20 watt tubes, or 0.45-0.9A for 1 x 20 watt tube, depending on the potentiometer setting. Here is the schematic diagram of the circuit:
The transformer is wound on a ferrite rod 10mm diameter and 8cm long. The diameter of the wire is fairly critical but has been successfully implemented using 0.28mm wire for all the windings in the prototype. When the circuit is operating, do not remove the tube as the spikes produced by the transformer will damage the transistor.