What a starter does and whether LED tubes need one

A starter is the small cylinder that ignites a fluorescent tube. How it works, how to tell when it has failed, and what happens to it when you switch to LED tubes.

Flick the switch and a fluorescent tube blinks once or twice before it settles. Behind that brief hesitation is a small, usually white or blue plastic cylinder inside the fitting: the starter. It is also behind one of the most common questions when switching to LED tubes: should the starter stay, be replaced, or be thrown away?

What the starter is for

A fluorescent tube cannot light straight away. The electrodes at its ends must first heat up, and then a short high-voltage pulse is needed to strike the gas discharge along the tube. With a magnetic ballast, these tasks are shared between the ballast and the starter.

Inside the starter is a small glass capsule containing neon gas and a bimetallic strip. When the switch closes, a faint glow discharge forms in the starter and heats the strip. The strip bends and closes the contact, so current flows through the tube's electrodes and heats them. With the contact closed, the glow stops, the strip cools and the contact opens. That sudden break in current makes the ballast produce a high-voltage pulse, and the tube strikes. Once the tube is lit, the voltage across it is too low to set off the starter again, so the starter stays idle until the next switch-on.

There is also a small capacitor in parallel with the bimetallic contact. It softens the spark when the contacts open and reduces radio interference.

When the starter fails

Many problems with fluorescent fittings come from the starter rather than the tube. Typical signs:

• the tube keeps blinking for a long time but never lights;
• the tube ends glow orange while the middle stays dark, meaning the starter contacts have welded shut;
• the tube lights, then periodically goes out and tries to restart;
• the starter smells burnt or its body has darkened.

The easiest way to test a starter is to swap in one that is known to work. It fits into its holder and locks with a clockwise twist, and comes out with an anticlockwise twist. Do this with the circuit switched off.

Starters differ by tube wattage and wiring. The body shows whether a starter is for a single tube or for two short tubes wired in series. The wrong starter makes ignition unreliable.

Electronic ballasts have no starter

Newer fluorescent fittings use a single electronic ballast instead of an electromagnetic ballast and starter. It controls electrode heating and ignition itself, and the tube lights without blinking, instantly or after a very short delay. These fittings have no starter holder, so the starter question never comes up when switching to LED.

You do not need to open the fitting to find out which type it is: the starter holder normally sits beside the tube on the visible part of the body.

What happens to the starter with LED tubes

An LED tube needs no heated electrodes and no gas discharge, so a conventional starter is useless to it. What you do with the starter depends on the type of LED tube.

When the LED tube is of the type that works with the existing ballast, you pull out the old starter and fit an LED starter in its place. It looks like an ordinary starter, but instead of a bimetallic strip and neon it holds a simple link that closes the circuit, usually with a fuse. Without that link the circuit stays open and the LED tube will not light. Leaving the old starter in place can make it keep trying to strike and cause the tube to flicker.

A direct-mains LED tube needs rewiring: ballast and starter are bypassed and taken out of use. The starter holder is left empty or taken out. Putting a starter into such a fitting by accident does nothing, but a label stating that the circuit has been modified prevents confusion later.

Quick summary

• Fluorescent tube with electromagnetic ballast: a starter is needed, of the correct type.
• Fluorescent tube with electronic ballast: no starter, none needed.
• Ballast-compatible LED tube in an electromagnetic-ballast fitting: replace the old starter with an LED starter.
• Direct-mains LED tube: starter and ballast are removed from the circuit.

The Zaferoğlu Elektrik catalogue includes an S2-type starter for fluorescent tubes. If your fittings still run fluorescent tubes, replacing a worn starter in good time protects the tube and reduces flicker at switch-on.