Light-emitting diodes (LEDs) started out at use in expensive laboratory equipment, but these days you can find them at work in everything from high-efficiency light bulbs to TV screens. In recent years, LEDs have evolved to be able to create any color of light using RGB mixing, a development that greatly expands their versatility and applications. Thanks to their low power consumption compared to their light output, demand for LED devices has never been greater. They’re so ubiquitous, in fact, that it can be easy to take them for granted. But what exactly are LEDs, and how do they work?
What is a diode and how does it work?
To understand LEDs, we first need to address diodes. Diodes are devices that allow current to flow in only one direction, which they accomplish through a process called "doping" a semiconductor. This doping process adds impurities to a mostly inert material (in terms of conductivity), changing the electron balance and creating the possibility of electron flow. Putting two versions of a doped semiconductor together establishes a one-way flow:
- N-type semiconductor: contains extra electrons (N-type) and one with extra impurities where electrons can go.
- P-type semiconductor: contains extra impurities through which electrons can travel.
The device remains inert below a certain voltage threshold, though. Without constant voltage, a neutral space called a depletion zone forms in between the N-type and P-type areas. To get the electrons moving, you'll need to connect the negative end of a circuit to the N-type and the positive to the P-type. If you do it the other way around, the depletion zone widens, which makes it very difficult to pass current through the device, hence the one-way flow.
What is a light-emitting diode?
In even the principle of basic diodes ― two sections of a semiconductor, one containing extra electrons and one containing extra electron holes that accept conducted electrons ―the device produces light energy every time electrons "fall" from the conduction band into the electron holes.
Diodes made from certain materials will cause electrons to "fall' farther, releasing a greater amount of energy that renders the light visible. The light's color is determined by:
1. The amount of energy the diode releases.
2. The specific materials that make up the diode.
For example, red and green LEDs have been available for decades, but in 2014 three researchers won the Nobel Prize for physics for their use of gallium nitride semiconductors to achieve the first blue-light LEDs. As a result of this discovery, "white light" LED arrays are now possible (such as for high-efficiency light bulbs). These arrays work by mixing red, green, and blue LEDs (the three primary colors of light) to achieve white.
Working of LED Lights
Diodes use two distinct sections of differently doped semiconductor to create a device with a one-way flow of electrons (and thus, electric current). One section contains electron holes, which receive electrons that fall from the conduction band and give off electromagnetic energy.
The term "LED" refers to diodes made with specific semiconductors that give off enough energy to produce (usually) visible light. Depending on the semiconductor material, the color of the emitted light will vary. With the relatively recent introduction of the elusive blue LED, we've seen a wide variety of new applications in development, including white-light LED light bulbs and LED screens.
To learn more about LEDs, check out our LEDs and Heat and 6 Key Considerations for LED Lighting Design articles on Arrow.com.