same wattage same voltage two cerise bulb is connect with
two phase it is complete the circuit and both will be glow
but if we connect with phase and neutral it also glow but
illumination is less then the the first method.
well dear, the glow of bulb will depend upon the phase angle between the phases.
if there is any phase difference, as generally happens in case of three phase system, then the bulb will glow, with the resultant frequency.