What is the function of the inductor in a fluorescent tube light circuit?

Answer 1

Without an inductor in series with the tube, the plasma in the tube would simply short-out the service wires. That would always cause the circuit's protective fuse to blow - or its circuit breaker to trip - to cut off the supply of current to the tube. If that happened the tube light would never be able to perform its intended purpose, which is to continue running - and giving out a continuous light - for long periods of time.

So a high-inductance choke must be used in circuit with the starter and the tube for two reasons:

• firstly the choke generates a high voltage pulse across the tube when the starter's contacts open. That pulse causes the gas in the tube to ionise and become a low-resistance plasma

  and

• secondly, because it is wired in series with the tube, the choke greatly reduces the current drawn by the tube once it contains the low-resistance plasma.

The starter is a special kind of switch: its contacts are made of a metal alloy which heats up and bends soon after a voltage is applied, causing the switch contacts to open.

Answer 2

The inductor - also called a "choke" - has two major roles:

1. Initially, in conjunction with the "Starter" it provides high voltage to initiate the plasma discharge through the Mercury vapor contained in the tube.

2. Secondly it reduces the voltage across the tube to a much lower level so as to prevent the tube from drawing so much current that it would just cause the circuit's protective circuit breaker to trip or the protective fuse in the circuit to blow.

A longer answer about the need for a choke and a starter

Without a high inductance choke in series with the tube, the plasma in the tube would simply short-out the service wires. That would always cause the circuit's protective fuse to blow - or its circuit breaker to trip - to cut off the supply of current to the tube. If that happened the tube light would never be able to perform its intended purpose, which is to continue running - and giving out a continuous light - for long periods of time.

The starter is a special kind of switch: its contacts are made of a metal alloy which, soon after a voltage is applied, heats up and bends, causing the switch contacts to open.

So a high-inductance choke must be used in circuit with the starter and the tube for two reasons:

• firstly the choke generates a high voltage pulse across the tube when the starter's contacts open. That pulse causes the gas in the tube to ionise and become a low-resistance plasma

  and

• secondly, because it is wired in series with the tube, the choke greatly reduces the current drawn by the tube once it contains the low-resistance plasma.