After ignition the operating current is regulated by the ballast. The inductance of a magnetic ballast not only limits the current, however, it also causes a phase shift between current and voltage. As a result both active power and reactive power are "consumed". Normal electricity metres do not measure this reactive power, although it does place a load on the grid. That is why public utilities require customers to use discharge lamps for compensatio
n for their electrical systems (with a few exceptions).
Capacitors can be employed to correct the phase shift between current and voltage. This works on the principle that a capacitor used for capacitance causes a phase shift in the opposing direction to that deriving from inductance. Capacitive ballasts can also be used to compensate the inductance of a corresponding number of magnetic ballasts.
In addition to power factor correction, Capacitors are also employed for radio interference suppression. This normally takes the form of an anti-interference capacitor connected in parallel to the terminal block.
The following circuit types are used to operate fluorescent lamps:
- Inductive Circuits for One Lamp
- Capacitive Circuits for One Lamp
- Compensated Circuits
- Dual Circuits
- Tandem Circuits