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Light Emitting Diode

Light Emitting Diode

A light-emitting diode (LED) is a diode that emits light when a current passes through it in the forward direction. It is a very useful display device. LEDs are available which emit light in different colors like red, green, and yellow. orange and white.

Light Emitting Diode Diagram

A Light Emitting Diode (LED) is typically made of semiconductor material, such as gallium arsenide or gallium phosphide. The typical structure of an LED is shown in the diagram below:
Light Emitting Diode


The LED is composed of a P-type semiconductor and an N-type semiconductor, which are brought into contact to form a P-N junction. When a voltage is applied across the P-N junction, electrons from the N-type semiconductor flow into the P-type semiconductor, and holes (absences of electrons) from the P-type semiconductor flow into the N-type semiconductor.

This flow of electrons and holes across the P-N junction causes a process called recombination, where electrons combine with holes and release energy in the form of photons, or light. The color of the light emitted by an LED depends on the materials used in the P-N junction, the LED will emit different colors based on the material used.

The diagram is a simplified representation of a LED, the actual structure may vary based on the type and application of the LED. It is important to remember that the LED is a polarized component, meaning it will only work correctly when the anode and cathode are connected to the correct voltage level.

Construction Of Light Emitting Diode

Construction Of Light Emitting Diode

The construction of a Light Emitting Diode (LED) typically includes the following main components:

  • P-N Junction: The heart of an LED is a P-N junction, which is a boundary between a P-type semiconductor and an N-type semiconductor. The P-N junction is formed by diffusing impurities into the semiconductor material to create a region with an excess of holes (P-type) and a region with an excess of electrons (N-type).
  • Anode and Cathode: The anode is the positive terminal of the LED and the cathode is the negative terminal. The anode is typically attached to the P-type semiconductor, while the cathode is attached to the N-type semiconductor.
  • Encapsulant: The encapsulant is a material that surrounds the P-N junction, it serves to protect the P-N junction from physical and environmental damage, and to improve the optical properties of the LED.
  • Lead frame: The lead frame is the metallic structure that connects the anode and cathode of the LED to external electrical connections. The lead frame is typically made of a conductive material such as aluminum or copper.
  • Lens: Some LEDs have a lens that is placed on top of the encapsulant to focus the light emitted by the P-N junction. The lens can be made of various materials, such as plastic or glass, and can have different shapes and patterns to control the light output.

Light Emitting Diode Working Principle

The working principle of a light-emitting diode (LED) is based on the phenomenon of electroluminescence. An LED is a type of semiconductor device that consists of a P-N junction, or a boundary between a P-type semiconductor and an N-type semiconductor. When a voltage is applied across the P-N junction, it creates a flow of electric current through the junction.

When the electric current flows through the P-N junction, it causes a process called recombination, where electrons from the N-type semiconductor flow into the P-type semiconductor and combine with holes (absence of electrons) in the P-type semiconductor. This recombination process releases energy in the form of photons, which are the particles that make up light.

The color of the light emitted by an LED depends on the materials used in the P-N junction. For example, an LED made with a gallium-arsenide P-N junction will emit infrared light, while an LED made with a gallium-phosphide P-N junction will emit green or blue light.

The efficiency of an LED is determined by how much of the electrical energy flowing through the P-N junction is converted into light energy and how much is wasted as heat. LEDs are very efficient, converting most of the electrical energy into light energy with minimal waste heat.

In summary, the working principle of an LED is based on the recombination of electrons and holes in a P-N junction, which releases energy in the form of photons, or light. The efficiency and color of the light emitted by an LED depend on the materials used in the P-N junction, and the design of the LED.

Light Emitting Diode Characteristics

Light-emitting diodes (LEDs) have several characteristics that make them unique and useful in a variety of applications:
  1. High efficiency: LEDs convert electrical energy into light with minimal waste heat, making them much more energy-efficient than traditional incandescent bulbs.
  2. Long lifespan: LEDs typically last for tens of thousands of hours, much longer than incandescent or fluorescent bulbs.
  3. Fast switching: LEDs can be turned on and off very quickly, making them useful for applications that require rapid flashing or strobing.
  4. Durable: LEDs are solid-state devices that are not fragile like incandescent bulbs and can withstand shock, vibration, and extreme temperatures.
  5. Low voltage: LEDs usually operate on low voltage DC power, making them safe to use and easy to install.
  6. Low heat emission: LEDs emit minimal heat compared to traditional incandescent bulbs, making them safe to touch and reducing the risk of fire.
  7. Color options: LEDs can be made to emit different colors of light by using different materials in the semiconductor.
  8. Directional lighting: LEDs emit light in a specific direction, which makes them useful for applications that require focused or directional lighting.
  9. Low maintenance: Since they last a long time and are durable, they require less frequent replacement and maintenance.

Light Emitting Diode Specifications

Light Emitting Diodes (LEDs) have a number of specifications that can vary depending on the application and type of LED. Some of the most important specifications include:
  1. Forward Voltage (VF): The forward voltage is the voltage required to forward-bias the LED and make it emit light. The forward voltage of an LED can vary depending on the type of LED, but it is typically between 1.8V and 3.6V.
  2. Forward Current (IF): The forward current is the amount of current flowing through the LED when it is emitting light. The forward current of an LED can vary depending on the type of LED, but it is typically between 10mA and 100mA.
  3. Luminous Intensity (Iv): Luminous intensity is a measure of the amount of light emitted by an LED, typically measured in millicandelas (McD) or candelas (cd).
  4. Color Temperature (CCT): The color temperature of an LED is a measure of the color of the light it emits, typically measured in Kelvins (K).
  5. Viewing Angle: This is the angle of view at which the LED emiLEDsght. Some LEDs have a wider angle than others, and this is an important specification if the LED is used in an application where the angle of view is critical
  6. Efficiency: LEDs are highly efficient light sources, converting most of the electrical energy into light energy with minimal waste heat.
  7. Lifetime: LEDs typically last for tens of thousands of hours, much longer than incandescent or fluorescent bulbs.
  8. Temperature range: LEDs can operate in a wide range of temperatures, from -40C to +85C, which makes them suitable for different environments.
  9. RoHS compliance: RoHS stands for Restriction of Hazardous Substances, it is a standard that regulates the use of certain hazardous materials in the manufacture of electronic devices. LEDs are commonly RoHS compliant, meaning they don't contain hazardous materials.

Light Emitting Diode Applications

  1.  LED is designed to produce coherent light with a very narrow bandwidth. The resulting called LASER diode and find application in an optical communication system and in the CD.
  2.  As an optoisolator (combination of LED and Photodiode in the same package).
  3. In-display devices player.

Light emitting diode Examples

Examples of common applications for light-emitting diodes (LEDs) include:
  1. Display screens on electronic devices such as smartphones, laptops, and televisions.
  2. Traffic lights, street lights, and other forms of outdoor lighting.
  3. Automotive lighting, including brake lights, turn signals, and headlights.
  4. Indicator lights on various types of equipment and machinery.
  5. Flashlights and portable lanterns.
  6. Holiday lighting and decorations.
  7. Backlighting for LCD displays.
  8. Medical equipment such as dental curing lights and phototherapy lamps.
  9. Growing plants in indoor gardens or greenhouses.
  10. Illumination for cameras and other optical devices.

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