The idea is simple, the secondary winding of Tr1 and T1 along with the associated components forms a high frequency oscillator circuit.
This oscillations forces an AC in the secondary winding of the transformer which is further induced into the primary of the transformer and stepped up to the corresponding rated value ofthe transformer.
The transformer used is an ordinary 12-0-12 volt 1Amp rated, it can be retrieved from any old, junk power supply unit that might be lying in your electronic junk box.
The transistor also is an ordinary type, here a 2N6101 is shown, but any other similar type will do. You may try a 2N3055 transistor or even a D1351 in place of the specified one.
The 2k5 preset is used for adjusting the frequency of the circuit which in turn affects the brightness of the connected tube.
The preset must be carefully optimized for obtaining maximum brightness on the tube and yet keeping the consumption on the relatively lower side.
The 0.47uF capacitor is also introduced for enhancing the output from the tube light, you may other nearby values for improving the overall brightness.
The battery can be a 12V, 7 AH battery which should last many hours.
However you cannot expect full striking brightness from this circuit. When I tested this circuit, I could never bring the tube light to its actual specified striking brightness.
The following diagram shows how to make a simple 20 watt fluorescent tube, emergency light circuit.