What is a Light Emitting Diode (LED)? - Definition & Applications

Instructor: Babita Kuruvilla

Babita has an electrical engineering degree and has taught engineering students and college students preparing for medical and dental college admissions tests.

In this lesson, we learn about light emitting diodes (LEDs), including what they are made of and how they work. We then explore their practical applications in our everyday lives.

What Are LEDs?

It's the holiday season and you're driving downtown to see strings of colorful lights strewn from lamp post to lamp post.

Holiday Lights
Holiday Lights

You take in the sight and admire the colors, wondering ''How do they make all those little bulbs in so many different colors?'' You remember hearing something about LEDs and decide to look them up when you get home.

So, what are these LEDs?

As the name suggests, light emitting diodes (LEDs) are diodes that emit light. Or, more specifically, LEDs are semiconductor electronic components that emit light. Let's take a minute to break that down.

What's a Semiconductor?

When a material conducts electricity, we call it a conductor, and when it does not allow the current to pass through, it's an insulator. We can engineer some materials to allow current to flow through only under certain conditions.

One way to do this is to add impurities into the material. Another is to change the temperature of the material. A material that has characteristics in between that of a conductor and an insulator is, fittingly, called a semiconductor.

These semiconducting materials are used to build electronics components for devices and appliances that we use daily.

What's a Diode?

How about a diode, then - what is it? A diode is a small electronic component used to build circuits, just like the ones in your phone or computer.

Diodes are very useful because they're made of semiconducting material, so we can control their behavior in the circuit. They also allow current to pass through in only one direction, which is great when designing circuits.

How Do Diodes Emit Light?

By definition, current is the flow of electrons. These electrons are negatively charged and high in energy. When an electron runs into a positively charged hole, the electron falls into the hole. When this happens, the electrons lose some of their energy in little packets of light energy called photons - this is the light that we see.

Depending on what semiconductor is used, these photons have different wavelengths. The wavelength of the light that is emitted determines the color we see.

There we have it! An LED is a light emitting diode that can convert electrical energy into light energy. By changing the semiconductor material from which the LED is made, we can change the color of the light emitted. That's how we make LEDs of different colors.

How Are LEDs Used?

Because LEDs are inexpensive, they have many applications, including in lighting and electronic/medical devices.


Compared to the regular Edison incandescent bulbs, LED bulbs have lower maintenance costs, last longer, and use less power, so more and more homes are switching to LED bulbs these days. High-power LED bulbs are also used in industries for brightly lighting large warehouses and workspaces.

Lights from LEDs are also used in many other ways:

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