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LEDs

LED is a broadly used semiconductor device that emits visible light or invisible infrared light when it is forward biased. In this article we will learn about LED, their uses, symbols and more.

Introduction

Light can be obtained from many sources such as candles, lamps and sunbeams etc. The light bulb was invented in 1879 by Thomas Edison. An electric current flows through a filament in the lightbulb, it heats up and emits light when enough current flows through the filament. This means that it converts electrical energy into thermal energy in a bulb. In light-emitting diodes (LED), electronic electrical energy can be converted directly into light energy.

Light emitting diodes (LED) are a standard light source that is widely used in electrical equipment. It has a wide range of uses ranging from mobile phones to large billboards. 

LED

A light-emitting diode (LED) is a semiconductor device which emits light when an electric current flows through it. When current flows through an LED, the electrons recombine with holes, which emits the light in the process. The LEDs allow current to flow in the forward direction and block current in the reverse direction.

Light emitting diodes are heavily doped p-n  junctions. Depending on the material of semiconductor used and the amount of doping, an LED emits coloured light with a specific spectral wavelength when it is forward biased.

LED Symbol

The LED symbol is the standard symbol for a diode having two small arrows which denotes the emission of light.

Work of LED

When the diode is forward biased, minority electrons are sent from p to n and the minority holes are sent from n to p. At the boundary of the junction, the concentration of the minority charge carriers increases. The extra minority charge carriers at the junction combine again with the majority carriers.

During recombination, the energy is released in the form of photons. With standard diodes, energy is released as heat. In the case of light-emitting diodes, on the other hand, the energy is released in the form of photons. This phenomenon is known as electroluminescence. Electroluminescence is an Optical phenomenon and also an electrical phenomenon in which a material emits light in response to the flow of electric current through it. When the forward voltage increases, the light intensity also increases and reaches a maximum.

Determination of Color of LED

The colour of an LED can be determined by the material used in the semiconductor element. The two main materials which are used in LEDs are aluminium gallium indium phosphide alloys and indium gallium nitride alloys. Aluminium alloys are used to get red, orange, and yellow light, and indium alloys are used to get green, blue, and white light. Slightly changes in the composition of these alloys change the colour of the emitted light.

Advantages of LED

There are many advantages of LEDs, some of which are given here.

  • Brightness of LEDs is controlled by varying the current
  • LEDs are small in size, weight is very light and are durable
  • LEDs are very cheap, easily available and the consumption of energy is low
  • LEDs can emit various colours of light
  • LEDs do not have toxic materials such as mercury (used in fluorescent lamps)

Applications of LED

There are many advantages of LEDs, some of which we will discuss here

  • LEDs are used in digital computers as well as in calculators
  • LED is also applicable in Traffic signals and Burglar alarms systems
  • LEDs are used in microprocessors and multiplexers
  • Led is also used in digital watches and smartphones

Layers of LED

There are basically three layers in a light emitting mode (LED) which are given as

  1. P-type Semiconductor
  2. N-types Semiconductor
  3. Depletion Layer or region

P-type semiconductor

In p-type semiconductors, trivalent impurities are added to the pure Semiconductor or intrinsic semiconductors. Holes are majority charge carriers of p-type semiconductor.

N-types semiconductor

In n-type semiconductors pentavalent impurities are added to the pure semiconductor. Free electrons are the majority charge carriers in n-type semiconductors

Depletion layer or region

Depletion layer is defined as a region or layer between p-type and n-type semiconductor in which no charge carriers (electrons or holes) are present. Depletion layer is a barrier to the current. To get rid of this barrier, we need to apply voltage greater than the barrier potential of this layer.

Conclusion

Light can be obtained from many sources such as candles, lamps and sunbeams etc. The light bulb was invented in 1879 by Thomas Edison.

Light emitting diodes (LED) are a standard light source that is widely used in electrical equipment. It has a wide range of uses ranging from mobile phones to large billboards. 

There are basically three layers in a light emitting mode (LED) which are given as

  1. P-type Semiconductor
  2. N-types Semiconductor
  3. Depletion Layer or region

LEDs are used in digital computers as well as in calculators.

LED is also applicable in Traffic signals and Burglar alarms systems.

Electroluminescence is an optical phenomenon and an electrical phenomenon in which a material emits light in response to an electric current flowing through it.