Over the years there has been this move to a new type of lighting bulbs known as LEDs. Which is short for Light Emitting Diodes. It is even making the CFLs (compact fluorescent lamps) look bad. CFL which we hailed as the next best thing to happen to technology is almost making incandescent bulbs go obsolete. While incandescent bulbs rely on electricity heating up an element (filament) to produce a glow, the CFLs uses electricity to drive a tube containing some gases (argon, and some mercury vapour) to produce luminance. The CFLs now stand a risk of being phased out by the famous LEDs.
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![led-1715226_1280.png](https://steemitimages.com/DQmchJRfw4jGtLqt8XKyXaFZTkYA21tzfe6YBnVJ8XgqRnS/led-1715226_1280.png)
<sup>[Image from Pixabay](https://pixabay.com/en/led-icon-logo-business-light-1715226/): Light Emitting Diodes</sup>


It would be proper to see what makes the LED tick.

We already know what LEDs are from their name; it is a special type of diodes that give off the light in the visible spectrum when electricity is applied to it.


From basic electronics classes, we are told that diodes are semiconductors that allows unidirectional flow of electricity. That is, it only allows electricity to flow in one direction and prevents reverse flow. It is like a one-way street that only allows movement in one direction. It has zero resistance in the forward direction but an infinite resistance in reverse direction.


<div class="pull-left"><center><img src="![2000px-PN_Junction.svg.png](https://steemitimages.com/DQmWSUjouKSaj1shJZTMwW5g8AB8Yjf7wEtPZvV4TMFHpNh/2000px-PN_Junction.svg.png)" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:PN_Junction.svg">Wikipedia Creative Common: PN Diode showing polarity</a></em></center></div>

A popular type of diode is referred to as the *p-n junction diode*. The boundary between the two is known as the p-n junction.


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#### Making an LED
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These p-n junction diodes used in power electronics and LEDs are made the same way. The only difference is one has material to enable you to see emitted light, and the other does not.


Making a p-n junction involves obtaining a highly pure semiconductor material. A semiconductor is a device with the properties that fall between insulators and conductors. Some of the semiconductor material include the popular silicon and germanium.
<div class="pull-right"><center><img src="![437341293_be6c2f3190_b.jpg](https://steemitimages.com/DQmSdPMzU5nWuCioZMSDmHGxU7U7TA4Q7xNMJaJxUKegCPX/437341293_be6c2f3190_b.jpg)" /><br/><em><a href="https://www.flickr.com/photos/oskay/437341293">Flickr Creative Common: A Power diode and two LEDs</a></em></center></div>

A semiconductor in its pure state or natural state is not suitable for electronic application due to its poor conductivity at room temperature. To make it suitable, a controlled amount of impurities are added in a process known as **doping**. When doped the semiconductor is referred to as an extrinsic conductor.


Getting a *p-type* semiconductor is done by adding impurities such as indium, aluminium or boron to produce an excess of positively charged carriers.

The *n-type* semiconductor is doped with arsenic or antimony to produce an excess of electrons (negatively charged carriers).

This arrangement ensures that electrons from the n-type semiconductor can always donate electrons to the p-type semiconductor.


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#### How it Emits Light
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There is a movement of electrons from the n-type semiconductor side to the p-type semiconductor side. 


<div class="pull-right"><center><img src="![2000px-PnJunction-LED-E.svg.png](https://steemitimages.com/DQmdqDgzc8VAJR2r8DH4K8S8fUCrFdYXuzLeW7yY4Aorocb/2000px-PnJunction-LED-E.svg.png)" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:PnJunction-LED-E.svg">Wikipedia Creative Common: Schematic diagram of a Light Emitting Diode (LED)</a></em></center></div>


This movement creates a change in the state of electrons. The electron moves around the nucleus of the atom pretty much the same way the earth moves (orbits) the sun. The electrons in different orbit have different orbital energy. This orbital energy decreases with increase in distance from the atom's nucleus.

As the electrons move, it would need to change its orbit which requires it either gives or loses energy to make this happen. Electrons going from a higher orbit to lower looses energy. That energy is in the form of light photons. That is how the diode emits light.

The higher the energy that was lost, the bigger the photons released and the brighter the light produced.


The frequency of the light photon is dependent on the energy that was lost and converted to light photons. Frequency within the human visible light spectrum is seen as light. But there are still LEDs that shows light that is not visible to human eyes. They are the type that is known as infrared LEDs and are used in remote control application, e.g. to control your tv's volume from your favourite couch.

https://steemitimages.com/DQmZYKHWL9fTQ3enbHELk91pmN3UX45EmaZowNi1wDLdYsz/For%20Quotes.png
Just a little trick you can try at home, although the infrared LEDs in remote controls are invisible to the human eye, you can still see the light they produce by using your phone's camera. Open your phone's camera. Point your remote at your phone's camera and press any button. You would see this invisible infrared light. 

This is simply explained by human eye's limitation to seeing electromagnetic radiation that is shorter than 730 nanometers ( visible light spectrum is from 390nm to 700nm).  The remote's IR wavelength is around 940nm. But the phone's camera does not have such limitations. If it did not work for you, try the front camera as some manufacturers block IR light on the back camera.
<div class="pull-right">Fun Exercise</div>
https://steemitimages.com/DQmadTLum9Npk6RMmzMVJnwBSvk5u6tTvc28ZEVy9Bord6L/DQmZYKHWL9fTQ3enbHELk91pmN3UX45EmaZowNi1wDLdYsz_1680x8400.png



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#### LED vs Incandescent
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LED bulbs are more efficient than the incandescent bulbs; it draws less energy.



<div class="pull-right"><center><img src="![Lightbulbs.jpg](https://steemitimages.com/DQmakK7nEHAMdze6EHZzKj2jrSwjpdhw77iBAJ1mXQHXMYT/Lightbulbs.jpg)" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:Lightbulbs.jpg">Wikipedia CC: Different Types of Bulbs</a></em></center></div>

E.g. a typical 40w, 130 lumens incandescent draws around 40w while a typical 580 lumens LED bulbs draws about 7.5w. Lumens, by the way, is the measure of how bright a lamp gives. The higher the lumen, the brighter the light.

The excess wattage is spent in heating up the incandescent bulb's filament that glows to produce light.

<div class="pull-right"><center><img src="![8229755738_5735ddb65a_b.jpg](https://steemitimages.com/DQmdEs9VrAdTJimp1NpdcnKjTpQKwzarcxzSykTY3wCXQPG/8229755738_5735ddb65a_b.jpg)" /><br/><em><a href="https://www.flickr.com/photos/carbonquilt/8229755738">Flickr CC BY 2.0: Carbon Footprint of LED vs Incandescent Bulbs</a></em></center></div>

That is not all, LED's are only energy-friendly and saves us tons of bills, they are also eco-friendly as they leave less carbon footprint compared to the incandescent bulbs.













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#### References
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[How PN Junction Diode Works](https://www.electronics-notes.com/articles/electronic_components/semiconductors/how-a-pn-junction-diode-works-basics-tutorial.php)




[Carbondioxide Footprint of Bulbs](https://static1.squarespace.com/static/54c8c11ee4b0b53cb9733f51/t/550584ede4b0fe6c8e8970b2/1426425069228/A-set-of-US-reference-images-methodology-v2.pdf)

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