This is basically a flasher circuit modified to turn a bulb on and off 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 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 seconds.