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What is Light Emitting Diode : Working & Its Applications


In the realm of modern technology, a small yet remarkable innovation has illuminated our world – the Light Emitting Diode (LED). This tiny semiconductor light source, born from the creative genius of Nick Holonyak back in 1962, has brought forth a revolution in lighting and displays. Let's embark on a journey to unravel the enchanting workings of LEDs and explore their diverse applications.


What is a Light Emitting Diode?


The light-emitting diode, known as LED, is essentially a p-n junction diode with specialized doping, crafted from unique semiconductor materials. In its forward-biased state, it radiates light, distinguishing it as a light-emitting diode.


LED Symbol


The LED symbol resembles a standard diode symbol with some unique modifications. The distinctive feature is the addition of two small arrows that point away from the diode's junction, indicating the emission of light. This modification signifies the LED's ability to emit light when forward biased, a fundamental aspect that sets it apart from regular diodes. In addition to the modified symbol, the


LED symbol also includes labels for its two terminals: the anode (+) and the cathode (-). These labels help engineers and technicians correctly identify the orientation of the LED when incorporating it into circuits.



Construction of LED


Substrate Layer: The LED's foundation is a substrate, typically made of materials like sapphire or silicon carbide. This layer provides mechanical support and thermal management, ensuring the LED's stability and efficient heat dissipation.


N-Type Layer: Over the substrate, a thin layer of N-type semiconductor material is deposited. This layer is rich in free electrons, which act as charge carriers. Materials like gallium nitride (GaN) are commonly used for this purpose.


Active Layer: Above the N-type layer lies the active layer, which plays a crucial role in the LED's light emission. This layer is often made of multiple quantum wells, extremely thin layers that facilitate the recombination of electrons and holes (positively charged gaps left behind when electrons move) – a process that generates photons of light.


P-Type Layer: The active layer is followed by the P-type layer, formed from semiconductor materials with an excess of "holes," or positively charged vacancies where electrons can move to. This layer facilitates the migration of holes, which contributes to the recombination process.


Contact Layers: Metallic contact layers are added to the N-type and P-type regions, serving as terminals through which electrical current is injected into the LED. These layers enable the controlled flow of charge carriers, setting the stage for light emission.


Encapsulation: To protect the delicate layers from environmental factors and to enhance light extraction, the LED is often encapsulated in a clear epoxy resin or a transparent material.


How does the Light Emitting Diode Work?


When a voltage is applied across the LED terminals – with the anode connected to the P-type region and the cathode connected to the N-type region – a forward bias is established. This bias enables the flow of electrons from the N-type region and holes from the P-type region into the active layer, creating a recombination zone. As electrons and holes recombine within this region, energy is released in the form of photons, producing visible light. 


Working Principle of LED

The operational essence of the Light-emitting diode (LED) is rooted in the principles of quantum theory. According to this theory, when an electron transitions from a higher energy state to a lower energy state, it emits energy in the form of a photon. This photon's energy is precisely aligned with the energy gap existing between these two energy levels. In scenarios where a PN-junction diode is forward-biased, permitting a preferred direction of current flow, an electrical current is facilitated across the diode.


Underlying Semiconducting Current Flow


The flow of current within semiconductors is intricately linked to the movement of charge carriers, specifically electrons and holes. These entities move in contrasting directions concerning the current flow. Consequently, a phenomenon termed recombination emerges as a consequence of these charge carriers' interactions.


This recombination process signifies the transition of electrons within the conduction band to the valence band. During this transition, as electrons leap from one band to another, they radiate electromagnetic energy in the form of photons. The energy level of these photons aligns with the forbidden energy gap intrinsic to the material.


A Quantum Insight


For illustrative purposes, let us delve further into the realm of quantum theory. The energy carried by a photon is a function of the Planck constant (h) and the frequency (f) of electromagnetic radiation. Mathematically, this relationship is expressed as:


Equation: E = hf


Here, h represents the Planck constant, while c symbolizes the velocity of electromagnetic radiation, equating to the speed of light. The frequency of radiation (f) and the velocity of light (c) are connected by the equation f = c / λ, where λ denotes the wavelength of electromagnetic radiation. Substituting these relationships into the equation results in:


Equation: E = hc / λ


This equation underscores the inverse proportionality between the wavelength of electromagnetic radiation and the forbidden energy gap. This phenomenon is particularly pronounced in materials like silicon and germanium semiconductors, where the forbidden gap between the conduction and valence bands engenders radiation primarily in the form of infrared waves. Notably, the wavelengths of infrared radiation lie beyond the visible spectrum, hence remaining invisible to human perception.


Applications of Light Emitting Diodes (LEDs)


1. LEDs find utility as bulbs in residential and industrial settings.
2. Light-emitting diodes are integrated into motorcycles and automobiles.
3. LEDs are employed in mobile phones for displaying messages.
4. LED technology is harnessed for traffic signal systems.




Thus, this article show an overview of the LED circuit working principle and application. I hope by reading this article you have gained some basic and working information of the light-emitting diode. If you want to purchase any LED light, could give a chance to Infralumin.

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