What is Light Emitting Diode (LED) Working, Advantages and Types of LED Explained

Today we will learn about the light-emitting diode, which is also commonly known as the LED. In many electronic devices, LEDs are commonly used. For example, today's LEDs are commonly used in smartphone displays as well as in-camera flashlights. Similarly, today's LED TVs are quite common. And then if we talk about lighting, then LEDs are used for lighting in houses and offices. And not only that, today, from the street lights to the traffic signals, or even for the display boards, LEDs are commonly used. 

So, in this video, let's understand the workings of the LED, different types of LEDs, and the advantages of the LED. And first, let's see the advantages of LED. Now, whenever LED bulbs are used for lighting, they are more energy-efficient than conventional bulbs. Also, the lifespan of these LED bulbs is longer than conventional bulbs. Then the third advantage of the LED is that it can be operated in a fast switching application. And the other advantages are the smaller size and the better controllability.

Here, controllability is in the sense that the brightness of the LED can be easily controlled. So, these are some of the advantages of LED lighting. So let's see the LED in action. So, as its name suggests, similar to the PN junction diode, it is also one kind of diode. But whenever the current flows through it in the forward direction, it emits light of a particular color. So let's understand the physics behind it. As we have seen in the earlier post of the PN junction diode, whenever it is forward biased, then the holes on the P side start moving towards the N side. And similarly, the electrons on the N side start moving towards the P side. And in a way, both holes and electrons contribute to the flow of current. And during the movement, these charge carriers are used to recombine with each other. So, in the PN junction diode, whenever these electrons and holes recombine with each other, they release energy in the form of heat. But in the case of the light-emitting diode, whenever they recombine with each other, they release energy in the form of light. And it can be further explained using the energy band diagram.

So, in the crystal structure, the free electrons have more energy than the electrons that are still in the valance orbit. And we can say that the free electrons are in the conduction band and the holes, or the empty space that is left by the free electrons, are still in the valance band. So, whenever the electrons and the hole recombine, the electrons from the conduction band come into the valance band. Or in other words, it comes from the higher energy level to the lower energy level. And as you know, whenever the electron jumps from the higher to the lower energy level, it releases energy in some form. So, in the normal PN junction diode, this energy is released in the form of heat. Because in the fabrication of this PN junction diode, different semiconductor materials like silicon and Germanium are used. And in these materials, during the recombination of the holes and electrons, the energy is released in the form of heat. On the other hand, in LEDs, during the recombination or the transition of the electron, the energy is released in the form of light or a photon. Because in the fabrication of the LED, different semiconductor compounds like GaAs and GaP are used. During the recombination of this type of semiconductor compound, the energy is released in the form of photons. And the energy of the emitted photon is equal to the bandgap.

That means the energy difference between this conduction and the valance band. And usually, this bandgap is represented in electron volts (eV). So, if Eg is the band gap, then the energy of the photon can be given as hc/lambda. Where h denotes the Planck's constant and C denotes the speed of light, the lambda represents the wavelength of the emitted light. So, as you can see from the equation, the wavelength is inversely proportional to the bandgap. So, by bandgap engineering, we can change the color of the emitted light. So, here is the list of the different semiconductor compounds that are used to generate the different colors of light. So, now if we talk about the electrical characteristics of the LED, it is very similar to the PN junction diode. And if you see the V-I characteristic of the diode, then it will be similar to the rectifier diode. But for the LED, the forward voltage drop is larger than the PN Junction Diode. So, for the PN junction diode, we know that the forward voltage drop is in the range of 0.6 to 0.7V.

But for the light-emitting diode, depending on the emitted color, the forward voltage drop can vary from 1.8 V to 3.5 V. So, as you can see from the graph, as we move from IR towards the blue light, the forward voltage drop of the diode will increase. So, for any LED in the forward bias condition, when the applied input voltage is greater than the forward voltage drop, the LED will emit light of the particular color. But without any kind of series resistor, the current that is flowing through the LED will be very high. And due to that, the LED may get damaged. So, if you see the datasheet of any LED, it will always mention the maximum forward current of the LED. And the current that is flowing through the LED should always be less than this limit. So, to restrict the current, the series resistor should always be connected to the LED. Alright, so here is the list of the different specifications of the LED that you will find in the datasheets. And we have already talked about the first three specifications.

That is the LED current, the forward voltage drop of the LED, and the wavelength of the LED. Let's talk about the last two specifications. Now, the brightness, or the luminous intensity, is usually defined for the LED at a specific current. And this brightness is defined in millicandelas. So, while selecting the LED for the specific application, one should also consider this specification. Then the other specification, which you will often find in the datasheet, is the viewing angle. So, basically, it defines the directivity of the LED. And if you see the datasheet of any LED, then you will find this type of polar radiation pattern for the LED. So, basically, it defines the angle from the maximum intensity where the intensity drops to 50 percent. So, for the given graph, the intensity is maximum at the center, and as we move away from the center, the intensity starts dropping in either direction.

At this point, the intensity is reduced by 50%. So, for this LED, the viewing angle will be equal to roughly 15 degrees. And if we consider the full angle, then it will be equal to 30 degrees. But in the datasheet, usually i, t, is specified as the half-angle. So, this is all about the different specifications of the LED. And last, let's briefly talk about the different types of LEDs. So, the first type of LED is the through-hole type of LED. And still, it is very popular among electronic hobbyists. And still, it is used in many applications. Then the second type of LED is the SMD LED. Or it is known as "Surface Mount LEDs." So, these types of LEDs are very tiny in size and are mounted or installed on the circuit board itself. And today, they are quite commonly used in LED bulbs and other applications. Then if we talk in terms of power, then there are high-power LEDs. So, these LEDs can handle much more current than normal LEDs. Therefore, they are much brighter than normal LEDs. But because of the large power dissipation, they are always used with the heat sinks.

Then the other type of LED is the COB LED. And it is known as the Chip On Board LED. As a result, it is very similar to an SMD LED. But here, so many tiny LEDs are installed on the same chip. Hence, it is much brighter than the other types of LEDs. Then the other type of LED that is commonly used today is the RGB LED. So, if you look at the through-hole type of RGB LED, it contains the four leads. So, if it is a common cathode type of LED, then it has a common cathode and three anodes for the different colors. That means three anodes for the RED, GREEN, and BLUE LEDs. And by changing the current through each LED, we can get different shades of color. So, these types of RGB LEDs are also available in SMD packages. And these types of LEDs are quite commonly used for decorative purposes. And last, let's talk about the alphanumeric LEDs. So, these types of LEDs are used to display the numbers and the alphabet in various industries. So, these are the different types of LEDs that are quite commonly used in today's world. So, I hope in this video you understand what LED is, how it works, and what the differences between