LEDs (Article)

Here at Instructables we love LEDs. They sip power, fit pretty much anywhere, are easy to wire up, and light up our projects with their many brilliant colors. Learning how to light one up is a valuable skill and can be quite addictive. So it’s about time we take a moment to think about these little bits of awesomeness and how they work.

This article is one in a series of Instructables articles about DIY technology. The full list can be seen here.

_{Photo by Q-Branch from LED Throwies}

Step 1: Making Light

LED is short for light-emitting diode and as such LEDs work like many other diodes. They are semiconductors that are made more conductive by adding impurities to material. For LEDs, these semiconductors are often gallium arsenide (GaAs), gallium phosphide (GaP), or gallium arsenide phosphide (GaAsP). These semiconductors are used to make wafers as thins as .5 microns or even less. Since one micron is one thousandth of a millimeter, thats pretty tiny.

When electricity is run through these wafers, we get light. With the current, electrons around the atoms get bumped to higher orbitals. As these electrons fall back down into lower orbitals they give off energy in the form of light. The bigger the energy drop the higher the frequency of light that will be given off. In other words, this determines the color of the light. A small drop and the light will be infra-red. A bigger drop will be in the visible spectrum and along with that the color of the light can also be controlled.

With these energy drops determining the color of the light the big question is how to make white light? After all, white light isn't one color, but the combination of many colors. One way would be to use an RGB LED and mix the red, green, and red colors to make white, but this requires some control of the different LEDs. The other method is to apply layers of phosphor on top of an LED, commonly blue, that shifts the wavelength of the light passing through it. It's not too different from how a fluorescent light works and is how many high-intensity white LEDs are made.
_{Photo by barney_1 from LED matrix using shift registers}

Step 2: Focus

Of course, these lights also need focus and that's assisted with the plastic lens that the diode is placed into. LEDs can have a narrow viewing angle or a wide one, depending on the shape of the lens. They can also be diffusive so that the light is more of a glow than a beam. The lens itself can also be tinted to help control the color of the light.

Put it all together and you have one tiny little light that is getting more efficient all the time. While LEDs have been used for indicator lights for a long time, their progression into the rest of our lives continues. Many flashlights and headlamps now use LEDs to provide long hours of light. The next step is for interior lighting. While LEDs are already used for accent lighting, it is only very recently that LED bulbs that go into regular light sockets are being sold in stores.

Despite all the technology it's easy to see the appeal of LEDs and even get started with them. Take one 5mm LED and a coin cell battery and slide the battery between the two wires. You'll have light! And if you didn't, just flip the battery around. Add a magnet and some tape and you have an LED throwie to stick to some metal. For now, just enjoy the glow and think of some places it would look good.



Useful links:
LEDs for Beginners - Get started!
LED Throwies - Simple, easy, and lots of fun
Light-Emitting Diode (LED) - More information about LED manufacturing

_{Photo by noahw from LEDs for Beginners}