Choke Coil in Tube Lights

Topics: Fluorescent lamp, Alternating current, Electric current Pages: 2 (516 words) Published: March 3, 2013
We saw in the last section that gases don't conduct electricity in the same way as solids. One major difference between solids and gases is their electrical resistance (the opposition to flowing electricity). In a solid metal conductor such as a wire, resistance is a constant at any given temperature, controlled by the size of the conductor and the nature of the material. In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles. In this way, current will climb on its own in a gas discharge, as long as there is adequate voltage (and household AC current has a lot of voltage). If the current in a fluorescent light isn't controlled, it can blow out the various electrical components. A fluorescent lamp's ballast works to control this. The simplest sort of ballast, generally referred to as amagnetic ballast, works something like an inductor. A basic inductor consists of a coil of wire in a circuit, which may be wound around a piece of metal. If you've read How Electromagnets Work, you know that when you send electrical current through a wire, it generates a magnetic field. Positioning the wire in concentric loops amplifies this field.

This sort of field affects not only objects around the loop, but also the loop itself. Increasing the current in the loop increases the magnetic field, which applies a voltage opposite the flow of current in the wire. In short, a coiled length of wire in a circuit (an inductor) opposes change in the current flowing through it (seeHow Inductors Work for details). The transformer elements in a magnetic ballast use this principle to regulate the current in a fluorescent lamp.

A ballast can only slow down changes in current -- it can't stop them. But the alternating current powering a fluorescent light is constantly reversing...
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