In the circuit shown in the figure, we add a capacitor (C2) and a resistor (R4) at the base of the power FET in order to extend the conduction time of the same when excited, and thus we have longer intervals for lighting the lamp. When the unijunction transistor produces the discharge pulse, it charges C2, which then slowly discharges through R4, keeping the polarized FET in conduction. The frequency can be adjusted by a potentiometer in series with the 100k ohm resistor (R1), or by changing the capacitor in the emitter of the unijunction. The lamp turn-on time can be changed either by changing the values of C2 or R4.
