Fluorescent lamp is used in portable lighting devices with fluorescent lamps (searchlight) in inverter circuit. A square wave is formed at the 3rd end of the 555 integral used in the circuit. It is possible to adjust the frequency of the square wave by the pot.
The refrigerated transistor, connected to the output of the 555, causes the continuous currents and transitions to pass through the transformer primary. Variable currents passing through the primary winding of the transformer lead to the formation of high-value AC in the secondary winding. Burns high-value AC fluorescent lamp in secondary.