Lamps and other electronic circuit which is work with dc voltage cannot work without the reactive power. Users generally believe that these devices only need active power but donn’t need reactive power, because they think it doesn’t work and it is useless. Of course, they take it for granted that the power factor of lamps and lanterns is 1 will be the best ad it can give maximum output power. However, it’s actually not ture.
If there is a lamp, there is no doubt that the circuit can not work normally if directly provided to the lamps and lanterns when rectified after inputing the ac mains, and geting pulsating dc voltage but do not to make any processing for the pulsating voltage . Enve though the power factor is close to 1 at this time. In order to make the circuit work properly, we must provide a smooth dc voltage to the lamps and lanterns. And the work of “smoothing” must be finished by the filter capacitor which is installed after the rectifier in the lamps and lanterns . This filter is just like a reservoir, the capacitor must be stored in a sufficient number of charge, and make the working voltage of circuit maintain a normal level and uninterrupted at the gap between rectifier half-wave. In other words, the voltage level of Uc has no significant change even if no input power between two pulse half wave, this function is accomplished by the energy storage within the capacitor, and the power stored in the capacitor is the reactive power. So, lamps and lanterns is to rely on reactive power to ensure correct use of active power. Therefore, lamps and lanterns not only need active power, but also need reactive power, both be short of one cannot implementation the normal use of circuit.