I have few unworking Compact Fluorescent Lights and i was wondering what is the output of the circuit?
The output is a high frequency sine wave. The voltage depends on the type of the tube. Typical voltages for CFL are 60V, but can vary vastly.
The oscillation is performed by folding back the current through the tube to the NPN transistors via the two secondary coils of T1. They are antiparallel, so only one of the BJTs can be operated at one time. L2 and C4 form the series resonator which provides a stable oscillation frequency.
During ignition R5 is conductive and closes the circuit via the (apparent) auxiliary electrodes. (Normally I expect a heating element in the bulb, but it is not indicated by any means).
The circuit elements on the lower left (Diac and 1n4007) may be for ignition phase, too, but I'm not sure yet.