What are LEDs?
LED stands for Light Emitting Diode. When powered correctly LEDs glow different colors. Some LEDs have only a single color while others have multiple color channels build in. Multi-channel LEDS can be mixed to create almost any color imaginable.
What do LEDs want?
- LED’s just want to glow.
- LED’s want only a SMALL amount of current — and they need it going in the right direction.
- They want the protection of a current limiting resistor.
LED Representation
The LED symbol combines a standard diode symbol (not all diodes glow) with outward pointing arrows to indicate light being emitted.
LEDs act like one way gates !
All diodes — whether they glow or not — act as one way gates. They only allow current to flow through them in one direction. We call this requirement for electrical direction polarity.
When an LED is given power in the wrong direction it will not light up (burn). So you must make sure to place the LED properly in your circuit.
Required Parts
At this point, you just need to grab your bag of LEDs.
Video :: Intro to LED landmarks
Slides: Grab a copy
Flat Side to Ground!
Our kit’s single colored LEDs have two physical characteristics that will help you figure out which way the electrons are allowed to flow and therefore how to place them in a circuit.
The best way is to determine polarity is to examine the bottom of the LED cap or lens (the colorful plastic bit). If you look very carefully at the bottom of the lens you should be able to find a flat region. You may have to feel for it with your fingers. The leg immediately below the flat region should always be connected towards (closer) to the ground side of your circuit.
An alternate way to figure out polarity is too look at the length of the legs of your LED. A fresh-from-manufacturer LED will have one long leg and one short leg. The short leg should be placed in a circuit facing ground. (BTW — eventually you or some ruthless electronics fairy will trim the legs of your LED and then the whole leg length system is completely useless — so make sure you can find the flat side).
Last, you may be interested to know that physicists gave the legs fancy names. The long leg is called the anode, the short leg called the cathode. If you can remember flat side to ground, I will forgive you for not remembering the fancy physics names.
All of this information is actually also summarized in the LED symbol. The triangle in the symbol points in the direction of current flow and the straight line right after the triangle acts like a wall or dam — it prevents flow coming from the flat side. The straight line also indicates the flat side of the LED lens. You have to admit, that’s pretty cool.
Note — in the image above, imagine current flowing from left to right.
Going Further
Check out Forest, an LED based installation by Micah Elizabeth Scott, created in collaboration with New Media students in 2015.
Also, Marshmallow Clouds, by tangible interaction and New Media students.
Ready to make an LED glow? Give this first circuit build a try if you have alligator clips — or — try the breadboard version of the circuit if you don’t!