Answer:
This is because electrical motors have starting current of 5 to 9 times the full load current, which causes sudden voltage sag in line and thereby flicker in lamps.
The light output from a incandescent lamp is directly related to the voltage.Hence a drop in system voltage will result in drop in output of the lamp
Note:Reason for high starting current in motor is due low power factor at starting due to large rotor reactance compared with rotor resistance.
