Fluorescent lamp is used in inverter circuitry in fluorescent lamps (flashlight). A square wave is formed at the end 3 of the 555 integrator used in the circuit. It is possible to adjust the frequency of the square waveguide with the pot.
The cooling transistor connected to the output of 555 causes constant currents to pass from the transformer primary to the transmission and cut. Variable currents passing through the primary winding of the transformer lead to the formation of high value AC in the secondary winding. High-value AC fluorescent lamp burns on the secondary.