Monday, 29 June 2015

How do Lightbulbs Work?

by Reetobrata Chatterjee

Lightbulbs are something that we walk past every day. With the flick of a switch, a dark gloomy room is transformed into a habitable environment. Imagine if lightbulbs did not exist and, as soon as the sunlight faded, you would have to whip out the trusty candles in order to see whether you were about to walk into a door or fall down the stairs. 

However, since the 1900s when the light bulbs became commercially available cheaply enough for the average guy, no one has had to face this problem. They were all probably too worried about catching tuberculosis anyway to ponder to long on this.

There are many different types of lightbulbs ranging from the classic incandescent kind to the more modern and high-tech LEDs.

Incandescent (the classic): The modern incandescent light bulb consists of 3 things: a long thin wire; a glass bulb and an inert Argon atmosphere so that you don’t have to fetch the ladder every week. The physics behind this is really simple. The current in the tungsten filament (the long thin wire) heats it up, causing it to glow. This glow travels through the bulb into your eyes. Next. 

Halogen (the common): This uses the same principle as the Incandescent lightbulb, being the thin tungsten filament, but it is built better in order to make it more efficient and longer lasting. The key difference is that along with the argon, it also has some halogen-based compounds such as Hydrogen Bromide. The main problem with the durability of the classic lightbulbs was that the tungsten would shoot off the filament (infrequently) and firmly deposit itself on the bulb. This meant that the filament lasted a smaller amount of time and over time the inside of the bulb became covered in tungsten, affecting the amount of light that got through. The Hydrogen Bromide effectively “captures” the stray tungsten atoms and returns them to the filament with some clever chemistry, which means the bulb lasts longer.

Sodium (the big): Sodium lamps are used in places like stadiums, sports halls and so on. Basically anywhere with a large room. These light bulbs are similar in the fact that they have a glass bulb. That’s it. Instead of a tungsten wire, they have vaporised sodium gas inside the bulb. As the current flows from one side of the bulb to the other, the Sodium atoms become excited (a technical term) and absorb some of the electrical energy and re-emit it as light. The main advantage these have over the fluorescent tube light kind (which work in basically the same way) is that these don’t emit much UV light. This means that the sports fans can watch the game in the stadium without the worry of dying from skin cancer, which is always a plus. 



LEDs (the future): These are tiny. They consist of a Semiconductor-based diode made from Gallium. A semiconductor is a special material which is not a conductor, but also not an insulator. Hence the semi-. The diode basically has 2 chambers. One where the current excites the electrons (in the same way as in the sodium lamp), and one where the electrons then relax, emitting the energy they absorbed before as light. These are better in almost every way compared to the Halogen and Incandescent bulbs. They are longer lasting, more power efficient and are usually brighter if they are of a similar size to the incandescent ones. 


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