How Does A Light Emitting Diode (LED) Make Light?

Posted by Jimmy Hovey on Wed, Mar 13, 2013 @ 14:03 PM

Understanding What's Makes A Light Emitting Diode (LED) Light...

It's not all that often that you find a great technical explanation that you can understand without being technical yourself.  That has been the theory behind our blog, explain things that people who aren't in the business can understand.  

I came across this article yesterday that was written in January and I think it does an excellent job of explaining the very technical aspects of LED lighting and how it works.

Normally, you would not insert an entire article within the text of my own article, but, in this case, they just do a really good job of explaining the technical aspects of a diode, the heart of an LED light source.  I didn't think I could do it any better myself, so I decided to take a part of their article and insert it here to share with you.  

The source for this article is HowStuffWorks "How Light Emitting Diodes Work"http://www.howstuffworks.com

Here's a portion of the article: 

What is a Diode?

A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that has had impurities (atoms of another material) added to it. The process of adding impurities is called doping.

In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms change the balance, either adding free electrons or creating holes where electrons can go. Either of these alterations make the material more conductive.

A semiconductor with extra electrons is called N-type material, since it has extra negatively charged particles. In N-type material, free electrons move from a negatively charged area to a positively charged area.

A semiconductor with extra holes is called P-type material, since it effectively has extra positively charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a positively charged area. As a result, the holes themselves appear to move from a positively charged area to a negatively charged area.

A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the diode, electrons from the N-type material fill holes from the P-type material along the junction between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow.

To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-type area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to the negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type material are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type material move the other way. When the voltage difference between the electrodes is high enough, the electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone disappears, and charge moves across the diode.

If you try to run current the other way, with the P-type side connected to the negative end of the circuit and the N-type side connected to the positive end, current will not flow. The negative electrons in the N-type material are attracted to the positive electrode. The positive holes in the P-type material are attracted to the negative electrode. No current flows across the junction because the holes and the electrons are each moving in the wrong direction. The depletion zone increases. (See How Semiconductors Work for more information on the entire process.)

The interaction between electrons and holes in this setup has an interesting side effect -- it generates light! 

OK, Did That Make Sense?

I didn't do so well in Chemistry and Physics, so I may still have to read this a few times to really get the hang of it.  All I know is that this is a really great lighting source that has come down considerably in price over the past 2-3 years.  It's not terribly important that you understand all the technical detail, but all you should remember is these things use very little energy, and last a very long time.  

In case that didn't make sense above, take a look at these graphics that www.howstuffworks.com created.  I think that helps too, check it out..... 

Light Emitting Diode Diagrams

Diagram 1- At the junction, free electrons from the N-type material fill holes from the P-type material. This creates an insulating layer in the middle of the diode called the depletion zone.


how-light-emitting-diode-works

Diagram 2-When the negative end of the circuit is hooked up to the N-type layer and the positive end is hooked up to P-type layer, electrons and holes start moving and the depletion zone disappears.

diagram-of-what-is-a-diode

Diagram 3-When the positive end of the circuit is hooked up to the N-type layer and the negative end is hooked up to the P-type layer, free electrons collect on one end of the diode and holes collect on the other. The depletion zone gets bigger.

 

understanding-how-diode-works

 

More LED Articles To Come

This is just one part of a series of posts put out by these folks at www.howstuffworks.com.  Be on the lookout for more articles like these in the coming days.  Oh, and since you likely won't remember, we will send you regular blog articles like these to you inbox, IF you give us your email address....and we will NOT spam you.  Just go over to the right column and give us your email, you'll be glad you did.  

However, if you are looking to learn more about energy efficient lighting, download our FREE eBook, full of useful information that should help you along your energy efficient lighting journey.   

business-owners-guide-to-energy-efficiency 

 

Here Are Some Other Articles We Have Written About LED:

How To Save Electricity: Energy Efficient LED Can Lighting Upgrade

400 Watt Metal Halide Replacements: LED Highbay vs. T5 Highbay

LED Light Bulbs: Everything You Ever Wanted To Know About LED

LED Industrial Lighting:New Energy Efficient Hazardous Area Lighting

 

Topics: light emitting diode, led diode, diode, diode led, what is a diode, diodes