To give a bulb a long life when its "flashed" on and off, they are operated at black heat, that is to say they have 70% of the working voltage put on them to keep the filaments hot(tish). I would suggest that you work out the circuit to see how this is done. It could be a resistor across the back of the switch. if you remove the resistor you may find that the black heat voltage goes. Could be that the switch changes the bulb voltage from , say 4 V to 6 V.
Frank