How does a fluorescent starter work?

A fluorescent light does not have the usual glowing filament of an incandescent bulb, but instead contains a mercury vapor that gives off ultraviolet light when ionized. The ultraviolet light makes particles that coat the inside of the tube, and these particles glow or fluoresce (see How Fluorescent Lamps Work for details).

Fluorescent starters are used in several types of fluorescent lights. The starter is there to help the lamp light. When voltage is applied to the fluorescent lamp, here's what happens:

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  1. The starter (which is simply a timed switch) allows current to flow through the filaments at the ends of the tube.
  2. The current causes the starter's contacts to heat up and open, thus interrupting the flow of current. The tube lights.
  3. Since the lighted fluorescent tube has a low resistance, the ballast now serves as a current limiter.

When you turn on a fluorescent tube, the starter is a closed switch. The filaments at the ends of the tube are heated by electricity, and they create a cloud of electrons inside the tube. The fluorescent starter is a time-delay switch that opens after a second or two. When it opens, the voltage across the tube allows a stream of electrons to flow across the tube and ionize the mercury vapor.

Without the starter, a steady stream of electrons is never created between the two filaments, and the lamp flickers. Without the ballast, the arc is a short circuit between the filaments, and this short circuit contains a lot of current. The current either vaporizes the filaments or causes the bulb to explode.

According to Sam's F-Lamp FAQ:

The most common fluorescent starter is called a "glow tube starter" (or just starter) and contains a small gas (neon, etc.) filled tube and an optional radio frequency interference (RFI) suppression capacitor in a cylindrical aluminum can with a 2 pin base. While all starters are physically interchangeable, the wattage rating of the starter should be matched to the wattage rating of the fluorescent tubes for reliable operation and long life.

The glow tube incorporates a switch which is normally open. When power is applied, a glow discharge takes place which heats a bimetal contact. A second or so later, the contacts close and provide current to the fluorescent filaments. Since the glow is extinguished, there is no longer any heating of the bimetal and the contacts open. The inductive kick generated at the instant of opening triggers the main discharge in the fluorescent tube. If the contacts open at a bad time, there isn't enough inductive kick and the process repeats.

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Originally Published: Apr 1, 2000

Fluorescent Starter FAQ

How does a fluorescent starter work?
A fluorescent starter is a simple timed switch that allows the flow of current in the filaments of fluorescent light. The current heats up the contact of the starter, turning its switch on and off until the fluorescent tube lights up. That’s why you see your fluorescent tube lights blink a few times before starting because the starter tries to maintain the flow of current.
Can a fluorescent lamp work without a starter?
Some modern fluorescent lights do work without a starter because they come pre-equipped with a ballast that has extra windings. It constantly supplies a small amount of voltage to give heat to the filaments.
When should I replace my fluorescent starter?
If your tubes aren’t efficient enough at igniting and have inconsistent lighting, that’s a sign you need to replace your starter. Another sign of a bad starter is that your tube takes longer than usual to start or flicker more often, signaling a malfunction.
Why do fluorescent lamp turns black?
If you notice the ends of your fluorescent lamp are turning black, that’s probably because it is rapidly switching cycles. Another reason could be a malfunctioning cathode inside the tube. Get your lamp replaced if you have a replacement warranty.
Which is better: LED or fluorescent?
LEDs are far better than fluorescents as they are more energy-efficient and generate more lumens per watt. Moreover, LEDs can last for more than 50,000 hours, have a greater wavelength and consume only one-fifth to one-third of the electric power of fluorescents.

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