This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit. The oscillation frequency is about 1Hz and is set by C1 value. The LED starts flashing when the photo resistor is scarcely illuminated. The onset of flashing can be set by trimming R2.
* Best results in flashing frequency can be obtained using for C1 a value in the 100 - 1000µF range.
* To drive a filament lamp make the following changes:
Use a 2.2 to 3V, 250-300mA bulb in place of the LED
R2 = 10K 1/2W T