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Light Emitting Diode (LED) Explained
Applications of the LED
So, today in many electronic devices in some or other way these Light Emitting Diode (LEDs) are commonly used. For example, today the LEDs are commonly used in smartphone displays as well as in-camera flashlights. Similarly, today the LED TVs are quite common.
And then if we talk about the lighting, then LEDs (Light Emitting Diode) are used for the lighting in the houses and the offices. and not only that today from the street light’s to the traffic signals, or even for the display boards, the LEDs are commonly used.
So, in this article, let’s understand the workings of the,
- different types of LED
- advantages of the LED.
Advantages of the LED
first, let’s see the advantages of the LED. Now, whenever the LED (Light Emitting Diode) bulbs are used for lighting, then they are more energy-efficient than conventional bulbs. Also, the lifespan of these LED bulbs is more than conventional bulbs.
Then the third advantage of the LED (Light Emitting Diode) is that it can be operated in the fast switching application. And the other advantages are the smaller size and the better controllability.
Now, here controllability is in the sense that the brightness of the LED (Light Emitting Diode) can be easily controlled. So, these are some of the advantages of LED.
Working of the LED
So, now let’s see the working of the LED(Light Emitting Diode). 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, then it emits the light of the particular color. So, let’s understand the physics behind it.
Now, as we have seen in the earlier Article of the PN junction diode, whenever it is forward biased, then the holes on the P side starts 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 used to recombine with each other. So, in the PN junction diode, whenever these electrons and holes recombine with each other, then they release the energy in the form of heat.
But in the case of the Light Emitting Diode, whenever they recombine with each other, then they release the 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 which are still in the valance orbit.
energy band diagram
we can say that the free electrons are in the conduction band and the holes or the empty space which is left by the free electrons is still in the valance band. So, whenever the electrons and the hole recombines, then the electrons from the conduction band comes 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, then it releases the 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 the electrons, the energy is released in the form of heat.
On the other end for the LEDs, (Light Emitting Diode) during the recombination or the transition of the electron, the energy is released in the form of light or the photon. Because in the fabrication of the LED, different semiconductor compounds, like GaAs and GaP are used. And in this type of Semiconductor compounds, during the recombination, 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 the electron volt (eV). So, if Eg is the band gap, then the energy of the photon can be given as hc/lambda Where h is Planck’s constant and the Cis the speed of light. And the lambda represents the wavelength of the emitted light.
Different LED Specifications
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 which are used to generate the different colors of light.
So, now if we talk about the electrical characteristic of the LED,(Light Emitting Diode) then it is very similar to the PN junction diode.
V-I characteristic of the diode
if you see the V-I characteristic of the diode, then it will be similar to the rectifier diode. But for the LED(Light Emitting Diode), 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, then the forward voltage drop of the diode will increase. So, for any LED(Light Emitting Diode), in the forward bias condition.
when the applied input voltage is more than the forward voltage drop, then the LED (Light Emitting Diode) will emit the light of the particular color. But without any kind of series resistor, the current which 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, then there is always mentioned the maximum forward current of the LED. And the current which is flowing through the led should always be less than this limit. So, to restrict the current, the series resistor should always be connected with the LED.
Also Read: Op-Amp: Voltage to Current Converter
Different Specifications of the LED
Alright so here is the list of the different specifications of the LED(Light Emitting Diode) which 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.
So, let’s talk about the last two specifications. Now, the brightness or the Luminous Intensity is usually defined for the LED (Light Emitting Diode) at the specific current. And this brightness is defined in the unit of millicandela. So, while selecting the LED for the specific application, one should also consider this specification.
Then the other specification which you 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(Light Emitting Diode), 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 then the intensity starts dropping in either direction.
And at this point, the intensity drops to50 percent. So, for this LED(Light Emitting Diode), 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 at the last, now let’s briefly talk about the different types of LEDs.
Also Read: Instrumentation Amplifier Explained
Type of LED
- hole type of LED
So, the first type of LED is the through-hole type of LED.
And still, it is very popular among the electronic hobbyist. And still, it is used in many applications.
- SMD LED
Then the second type of LED(Light Emitting Diode) is the SMD LED.
Or it is known as the Surface Mount LEDs (Light Emitting Diode). So, these types of LEDs are very tiny in the size and they are mounted or installed on the circuit board itself.
And today they are quite commonly used in LED (Light Emitting Diode) 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 the normal LEDs.
And therefore they are much brighter than the normal LEDs. But because of the large power dissipation, they are always used with the heat sinks.
- COB LED
Then the other type of LED (Light Emitting Diode) is the COB LED. And it is known as the Chip On Board LED. So, it is very similar to the SMD LED.
But here so many tiny LEDs (Light Emitting Diode) are installed on the same chip. And hence it is much brighter than the other types of LEDs.
Also Read: OP-Amp Comparator & applications Explained
- RGB LED
Then the other type of LED (Light Emitting Diode) which is commonly used today is the RGB LED. So, if you look at the through-hole type of RGB LED then 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 LED(Light Emitting Diode). And by changing the current through each LED, we can get different shades of color.
So, this type of RGB LED (Light Emitting Diode) is also available in the SMD packages. And these type of LEDs is quite commonly used for decoration purpose.
- alphanumeric LEDs
And at the last let’s talk about the alphanumeric LEDs. So, these types of LEDs(Light Emitting Diode) is used to display the numbers and the alphabet in various industries.
So, these are the different types of LEDs(Light Emitting Diode) which are quite commonly used in today’s world.
So, I hope in this Article you understood what is LED(Light Emitting Diode), how it works, and what are the different types of LEDs(Light Emitting Diode). So, if you have any questions or suggestions, do let me know here in the comment section below.
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