This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying the preset VR1.
The ON time of the circuit is given by:
TON= 0.69xC1x(R1 + VR1) second
and the OFF time is:
TOFF= 0.69xC1xVR1 second
You can increase the value of C1 to 100uF to get a slower flashing rate of upto once in 10 sec.