Fluorescent starters or glow starters are used to help fluorescent tubes and lamps ignite in the initial starting stage of their operation.

Simply put, fluorescent starters are a timed switch. The switch opens and closes until the fluorescent tube ‘strikes’ and lights-up. If the fluorescent tube does not light, the switch repeats it’s open/close cycle and the fluorescent tubes attempts to ignite again.

Read on if you would like to know more about this process…

When power is first applied to a fluorescent fitting, the current creates two electrodes inside the fluorescent starter to heat and glow. This causes one of the electrodes in the fluorescent starter to bend towards and make contact with the other electrode. This closes the switch and the current now passes through the fluorescent starter and on to the rest of the fitting. This means that the circuit across the fluorescent tube and the ballast in the fitting will effectively be switched “in series” to the supply voltage.

The current that is now flowing into the fluorescent tube causes filaments at each end of the fluorescent tube to heat up and begin to emit electrons into the gas that exists inside the fluorescent tube by a process known as thermionic emission.

Inside the fluorescent starter, the touching electrodes short out the voltage sustaining them and they begin to cool down and bend away from each other. This then opens the switch within a second or two.

The current through the filaments in the fluorescent tube and the ballast is then interrupted, and with the circuit no longer in series, the full voltage is applied to the fluorescent tube filaments and this generates an inductive kick which provides the high voltage required to start the fluorescent tube.

If the filaments were not hot enough during the initial cycle, then the fluorescent tube does not light, and the cycle repeats with the starter heating up and closing the circuit again.

Several cycles are usually needed to ignite the fluorescent tube and this causes flickering and clicking during the starting stage.

Once the fluorescent tube strikes, the starter switch does not close again because the voltage across the lit fluorescent tube is insufficient to re-start the heating up process of the electrodes in the fluorescent starter.

The older the fluorescent tube is and the older the fluorescent starter is, the less efficient they are at igniting. A tube that takes more than a few seconds to start-up is a clear indicator that the tube and starter may need replacing.


Types of Fluorescent Starters

Fluorescent starters can be identified by a designated wattage written on the side. The wattage is directly related to the length of the fluorescent tube it is designed to work with.

Listed below are the 3 most common types of fluorescent starter:


  • Series Twin Tube FS2 Series Starter Up to 22W – For use with fluorescent tubes when used in 600mm x 600mm ceiling panels with multiple tubes (generally found in offices and similar commercial applications).
  • Single Tube Starter 4W to 65W (FSU-10)  – Commonly used for 2ft 18W, 3ft 30W, 4ft 36W and 5ft 58W fluorescent tubes.
  • Single Tube Starter 70W to 125W (FS125)  – Commonly used for 6ft fluorescent tubes of 70W and over.

2D Lamps and T9 Circular Lamps

As a general rule, lamps with 2-pins have the starter built into the body of the lamp but 4-pin versions need an external fluorescent starter.

When replacing a 2D or circular lamp make sure you replace like-for-like with the appropriate wattage.


How do you know if you need a new starter?

  • A flickering fluorescent tube.
  • The fluorescent tube does not light.
  • Fluorescent tube lights at one end only.
  • Fluorescent tube lights at the ends only but not in the middle.

When considering re-lamping an area with multiple tubes we suggest replacing all the old tubes for new.

Older tubes lose colour and can appear dull over time. New ones alongside will look brighter and cleaner.

Re-lamping all the tubes in the room together will give an overall uniform appearance.

Make sure you read our handy guide to replacing fluorescent tubes.

We also advise replacing all fluorescent starters whenever you replace a tube. This ensures a prompt and efficient start-up, promotes maximum performance from the tube and can extend tube life.

Please note that LED tubes are supplied with their own special starter – which is essentially a circuitry which bypasses the function that a normal fluorescent starter would perform (LED tubes do not need to “heat up”). NEVER use a fluorescent starter with an LED tube.

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