Saturday, September 17, 2011

Lamps Get Dark Circles Too!

Fluorescent lamps sometimes have these dark rings. They usually form around the edges. Lamps usually go bad after they get these dark rings.

What are they? Why do they form? Why are they bad?

Let's first see how a fluorescent lamp works. It works by converting energy from electricity to light. To do this, it uses some special gases inside the tube. So how do the gases do it?

The gases, or for that matter anything in this world, is made up of tiny things called atoms. Inside atoms there are even smaller things called electrons, they can't be seen, only imagined. It is possible to excite the electrons by giving them energy. What do they do when excited? They jump around inside the atom! When they are very excited, they can even fly out of the atom and hit another atom. Ok... but then so what? You ask.

Atoms seen under microscope (left).
You can imagine the parts of an atom like this (right)

Well, that's where the magic happens! You see, the electrons eat up the energy you give them, like heat or electricity, and then they dance around. While dancing around, they give out the energy they absorbed, but this time in the form of light. So, with all their dancing and jumping, they are actually helping us convert electricity to light!

Aha! But then, what about those dark rings?

Ok… So here's what is there inside the lamp. The lamp is filled with a special gas. On each of the ends of the tube are metal conductors. They are called electrodes. They also have small heaters to heat them up. And they are coated with a special material whose electrons get easily excited through heat.

We apply electricity to these electrodes on each of the ends which also heats them up. The electrons of the electrodes get excited. They jump around, hit their nearby atoms, which are the gas atoms. The gas atoms get excited and excite their nearby gas atoms. So on and so forth, till all atoms inside the tube get excited and start jumping and flying around, giving us light.

But everything's not hunky dory everywhere. Remember the special coating on the electrodes? All these jumping and flying electrons around the heated electrodes, slowly wears it out. It's called sputtering. You can imagine how oil sputters on a pan or water boils into steam. Similarly, the coating slowly comes off the electrodes. The sputtered coating gets deposited on nearby things, in this case the glass cover. That's how the glass gets the dark marks near its ends.

Are the rings bad for the lamp? Yes… When most of the coating wears out, the electrodes can no longer excite enough atoms. A worn out electrode can even break. When that happens, the gas atoms can not get excited enough. And then the lamp won't light up any more. This happens normally with age. But it can happen more if the light fixture is faulty.

Here are a few more things for you to ponder on:
  • Why are the lamps coated white? Hint: Why are they called 'fluorescent' lamps?
  • Why do some lamps flicker before switching on?

Photo credits:
  • Wikipedia


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  2. LOL! Love the article.Quite an informative post!! :)
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