Fluorescent Light: How it work?Need of ballast & starter

When there is electricity, the first electrical appliance comes in our mind is a Light. Electrical lights are used by everyone whether it is a small house or a giant factory. From centuries we are using electrical lights. Humphry Davy demonstrated the first electric lamp in 1809. Then Thomas Edition patented the carbon-thread incandescent lamp on 1879.  Mercury-vapor lamp which is the base of Fluorescent light bulbs was 1st came into the picture in 1901 by Peter Cooper Hewitt. But officially the patent of Fluorescent Lamp was taken by Edmund Germer in 1926. Since then so many advancements are implemented on the Fluorescent Lights, and today we are using an optimized appliance which is brightening the darkness much perfectly by using comparatively less power.We will cover all about the Fluorescent Light here.

What is Fluorescent light?

I am going to make it very simple for you to understand. To know it right from the basic you need to know “What does the word Fluorescent mean? And before falling for the word fluorescent, I’ll discuss in short about luminescenceincandescence.

What is luminescence?

The cold bodies(not heated) that emit lights are called luminescent. Some crystals or stones are luminescent. Light comes out from those materials might be because of some chemical reactions or subatomic motions going on inside these materials. In some navigational & aviation instruments and also in the dial and hands of watches these luminescent materials are coated which can be visible in darkness also. Light comes out form Fireflies is also an example of luminescence.

What is Incandescence?

The word Incandescence is derived from the Latin verb incandescent, which means Glow White.

When a hot body glows as a result of temperature, it is called incandescence. Incandescent light exists till the body is hot and the light diminishes with decreasing temperature of the body.



Incandescent Lights were invented before Fluorescent light and which glows when the filament of this light gets heated by the flow of high current through it.

Fluorescent Lamps are invented to overcome the disadvantages of Incandescent lights which are

  • Incandescent lamp generates high temperature.
  • Consumes more Energies. By using Fluorescent bulbs, we can save electricity.
  • We can not generate light of different colors for decoration purpose.
  • The lifetime of an Incandescent bulb is lower.

What is Fluorescence?

Fluorescence does not have its light like Luminescence. Also, it does not glow due to the heat. This kind of materials absorb radiation from others and then re-emit it.

The Fluorescent light has a longer wavelength than the light it absorbs. Therefore it has lower energy than the absorbed radiation. Generally Fluorescent material absorbs UV radiation and then illuminates.

The fluorescent lamp also works on this principle. The low-pressure vapor tube has fluorescence material covered in the inner wall of the glass tube, which emits light once after absorbing UV light which generates by a chemical reaction when current flows through it. We will discuss below that how does it work…!!

Different Parts and Structure of Fluorescent lamp

Fluorescent Light diagram


  1. It has a sealed glass tube. The tube is filled with Inert gas(Argon generally) at a very low pressure.
  2. A tiny amount of mercury drop is present inside the glass tube.
  3. The inner wall of the glass tube is coated with phosphor powder which is a fluorescent material and white, That is why the tube looks white to us.
  4. There are two filaments made of tungsten present at each end of the tube which act as electrodes. One as positive electrode or Anode and another as negative electrode or Cathode.
  5. Ballast to regulate power across the electrodes.
  6. A Starter.Ballast and starter of Fluorescent Light bulbs

How does Fluorescent light work?

The working principle of Fluorescent lamp is quite complicated but not difficult to understand, and I found it very interesting. For your easy understanding, I will first describe the main light and how it works..! Then we will move on to the Ballast and Starter and discuss the use of these two devices in the circuit of Fluorescent Light bulbs. Don’t forget to read about the Use of Starter, Starting up a Fluorescent light is the most complex as well as an interesting process of it.

So basically the glass tube of the Fluorescent Light has two electrodes at it’s each end. One acts as Anode and other acts as Cathode when the lamp is connected to the ac power source. One holds the positive charge, and another holds the negative charge. So an electrical potential difference develops across the two electrodes of the tube which is filled with inert gas(Argon in general) at very low pressure. This potential difference and very low pressure cause the break down of the gas molecule and release free electrons which can carry current. This process is called ionization. As we know inert gas has the maximum number of electrons in its outer valence band; it can be a good conductor when ionized.

Up to this, we have discussed the simple electronic process of gas tube discharge by which charge flows from one electrode to another electrode. But this current flow is not the light we get from a Fluorescent lamp. There are some more processes takes place inside the tube, and all in combined generate the light.

Next, the role of Mercury takes place inside the Fluorescent tube. The two electrodes of the tube get heated as the current flowing through it. The small amount of mercury which is present there in the glass tube changes from liquid to vapor due to the higher temperature and the charge inside the tube. As the ions of inert gas move inside the tube from one electrode to another, some of those collide with the gaseous mercury atom. This collision produces some energies and those energies get released and become a radiation UltraViolet rays. The frequency of UV light is very high, and the wavelength is so small that it can not be visible by the human eyes.

So far we knew up to the UltraViolet light generates inside the Fluorescent lamp. But UV light has no use as it is not visible, It can not give us the light we need. Here the Phosphor coating in the inner wall of the glass tube comes in picture. The phosphor is a Fluorescence material. So it absorbs radiation and then re-emit it with higher wavelength than the original radiation. So the Phosphor coating absorbs the UV light and radiates the final light that we can see coming out from a Fluorescent lamp. After all these sequential processes we get bright, clear and cool light from Fluorescent light bulbs.

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Starter and Ballast

We knew how the light glows. But we can not ignore the role of Starter and Ballast that is present and connected with Fluorescent light. Without the Starter the Fluorescent Lamp will not start, or even it started by chance, it will flicker or fail to provide a continuous flow of light. Without a Ballast also the light won’t start as it provides the higher voltage to the light to start. Ballast also control the current through the tube to protect it from short-circuiting.

Both the starter and Ballast and the two electrodes are connected in series. See the diagrams for clarification.

Need of Starter in fluorescent light

We know that gas is not a good conductor of electricity. But a high voltage across the gas can ionize the gas, and it will start conducting. And the amount of the voltage by which a gas will get ionized is depended on the temperature of that gas. A colder gas has higher resistance and needs comparatively more voltage across it to be ionized. But creating a higher voltage may be difficult and also quite dangerous. So without going for a higher voltage, it is preferred to preheat the gas inside a Fluorescent tube before its ionization. Also, the distance between the two electrodes of a fluorescent lamp is high, so it is difficult to ionize the cold gas inside it even though we provide a higher voltage to it. So the gas inside the tube needs to be preheated.

How does Strater work?

Starter acts as a timer switch of the circuit. It is also a small tube of  1 watt and contains Neon or argon gas inside it, and inside the tube, there is a metallic strip which can expand and flip back when it is subjected to heat. In short, it is a switch which is closed when it is heated and opened when it is cold.

The metallic flip switch gets opened, or it does not connect the path. But when we switch on the Fluorescent light, a potential difference generates across both the glass tube(Tube of the fluorescent light and the tube of the starter). But the distance between the two electrodes of the Fluorescent light is much higher than the distance between the two terminals of the stater. So the gas inside the stater get heated immediately by the potential difference across it and because of this heat, the metallic strip expands and touch the other end, or it closes the path. In a result, current flows through the starter and not through the Fluorescent lamp Tube.

See the Picture below.

Starter Closed

Initially when the power supplied to this circuit, Current will not flow through the tube. Current will be bypassed through the starter as it will get heated immediately and the metallic strip will be triggered.

When the starter switch is closed, current will flow through it as well as through the two electrodes of the lamp. As those two electrodes are made of tungsten, it will be heated quickly and pass it’s temperature to the gas molecules around it. In this way, the temperature of the gas inside the tube of the Fluorescent lamp will rise up.

There will not be any potential difference across the terminals of the starter when current will be flowing through it, as it is shorted. The drop in potential will cause the drop in temperature within 1 or 2 seconds. And as the temperature is gone, the metallic strip again flip back and disconnect the current flow.

When the starter gets disconnected, immediately a high voltage will be kicked by the ballast. Because the ballast has a transformer and when suddenly the flow of current stopped, the magnetic field of the transformer will be collapsed, and a high inductive voltage will be generated. This voltage will ionize the gas inside the tube of the fluorescent Lamp which is already heated. And then the current start flowing from one electrode to another inside the tube.

If the two electrodes could not get enough voltage from the ballast when the starter turned off, then the gas inside the tube will not be ionized, or the lamp won’t get started. And if the Lamp did not start, the starter again experience the potential difference across it’s terminal, and it will gain temperature again. The metallic strip will again flip to make the path closed. This process will go on until the gas inside the tube of the lamp will not get heated enough to be ionized.

Starter opened

The gas inside the tube got ionized. The starter switch remains open.

Once the gas inside the tube will get ionized by the kicked high voltage from the ballast when the starter switched off, all the current will start flowing through the glass tube of the Fluorescent lamp. So the Starter will not experience any potential difference across it again. And the starter will remain open.

Watch this animated video to clear your concept.

Need of Ballast

  1. 1Ballast has a very important role in starting the lamp and protecting it from the high current. When the metallic strip of starter flips back or when the starter switch turns off, the ballast provides high voltage through the electrodes of the Fluorescent lamp.
  2. When the gas inside the tube of Fluorescent light got ionized current start flowing through the tube from one end to another. At this time Ballast limit, the current through it. If it does not limit the current, the path will get shorted and a high amount of current start flowing through the tube. Which will either melt down the tungsten coils or explode the Glass tube.

How does Ballast work?

Inside the ballast, there is a step up transformer which provides high voltage during the starting up of the Lamp. And it has a reactor or choke inside it which limits the current flowing through it.

Magnetic ballast has a transformer to control the power. The coil of the transformer work as an Inductor. When current flows through the inductor, magnetic field generates. And a magnetic field always opposes the change in current flow. This way it limits the growth of current in the circuit.

Modern Fluorescent Lights

The fluorescent light we use now is way much advanced than it was discovered. It is designed for higher efficiency with consuming lower power. The size is also compacted. The CFL  we use nowadays is also Fluorescent lamp which uses coiled glass tube and electronics compact ballast.

The use of the starter is also deprecated. Modern Fluorescent light use pulse starts technique to start the lamp and this pulse starting components are embedded inside the ballast itself. It is called rapid start lamp. Here ballast sent channeled and configured the current to the electrodes continuously to get it heated.

Electronics ballast is used which is compact and use no magnetic or inductive techniques to limit the current flow. It uses semiconductors to do the same job. Where the Magnetic ballast was using the transformer to control electric power.

Advantages of Fluorescent Light

  • It is cheaper than other lights. The Ballast is quite expensive, but it lasts for long. We have to change the glass tube of the light which is around 60% cheaper than other lights.
  • The light from a Fluorescent bulb does not generate heat as much as an incandescent lamp generates.
  • This lamp lasts longer than the other lamps. It works for around 9000 hours. After a long period when the mercury inside it gets completely dissolved with other gas, It starts flickering and stops. Sometimes the tungsten filament also burnt out due to higher current flow.
  • We can get Fluorescent lights of different colors. For the household purpose, there are lights available in two colors. warm white and cool white. But for decoration purpose, we can have lamps of the color red, green, pink, yellow, etc.
  • It produces diffused lights. It does not create any clear shadow of objects.

Disadvantages of Fluorescent Light

  • Installation cost is higher. Initially, we need a stand, ballast, starter and a tube, altogether cost three times higher than other lights.
  • It flickers at the time of starting which can be bit irritating. and if we stare at the flickering tube, it may cause strain, headache, and pain in our eyes.
  • Flickers a lot at the end of the lifecycle when there will not be sufficient mercury left in the tube.


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  1. priyadarshi sahoo October 14, 2017
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