Light Emitting Diode (LED)

Light Emitting Diode (LED) :

Light Emitting Diode is one of the semiconductor diode, which emits light when a corrected supply is passed to the LED in a forward direction of the devices.

History :

The first LED (Visible Spectrum) was invented by the scientist Nick Holonyak jr in the year of 1962. Year by year, the technology was developing rapidly, means the advantages also increases in LED’s. The cost of LED’s getting less and the with more quality. In the year of 2011-2012 the manufacturing products increased. LED products replaced other bulbs by 22% among the world products. 

Principle :

The basic principle involved in LED ,  in a solid state material, the form of electroluminescence where incoherent and narrow-spectrum light is emitted from the PN junction.

About :

The emitting  color is based on the combination and conditions of the semiconductor device used. The emission may be infra-red, visible, ultra-violet. The size of the light source LED  is less than 1 square millimeter. Though it’s a light emitter there are some more useful applications are also available. Some of them are sterilization of water using  UV- LED, Disinfection of electronic devices, and as a grow light to enhance photosynthesis in plants.

Specifications :

The junctions of the diode must be optimized and the proper semiconductor should be used to emit light which can be seen externally. Pure gallium arsenide emits energy in infra red portion of the spectrum. For a visible red color, aluminium is used in the top of  Gallium arsenide, which is called is aluminium gallium arsenide. For an emittion of  pure red color  phosphorous is added. Like a same way, gallium phosphide emits green color, aluminium indium gallium phosphide which emits orange and yellow color. In common many of the LED’s are based on gallium semiconductor.

Construction & Working : 

  

Light  Emitting  Diode normally consists of some layer of semiconductor material which s added with some impurities into a pure semiconductor to form a PN junction. Generally LED’s are constructed using Gallium arsenide(GaAs), Gallium arsenide phosphide(GaAsP), or Gallium phosphide(GaP) and other group like III-V components. These above mentioned semiconductor are called as direct band gap semiconductor which forms compound junction between them. The common semiconductors like silicon and germanium is a simple element called indirect band gap semiconductor which forms simple junction between them. It does not emit light like direct gap semiconductor. Instead of light, heat will be released from that LED’s. 

The diagram of LED is shown below to this paragraph. When the LED is in forward bias, the electrons flows through N-type to P-type materials and the currents flows through P-type to N-type and it will not happens in the reverse direction. When the electrons meet the holes at the junction the electrons gets fall from higher energy band to lower energy band and it automatically gets recombined with the hole. The energy is released in the form of photon of wavelength which is equal to band gap of the semiconductor due to the recombination.

Advantages of Light Emitting Diode :

Normally the life time of LED is high comparing the other Light Emitters. It works for 50,000 hours or more than that if it is engineered properly.

The energy efficiency is high, which has the capacity to emit up to 135 lumens/watt.

Using LED we can use it in the directed place, so that there is no wastage of light energy.

LED does not bother about the temperature, as it works in any of the temperature(high temperature or low temperature).

It emits light instantly, in nano seconds.

LED are also called as Solid State Lighting(SSL). These are made using  solid material and not  using filament, tube, bulb which is breakable.

LED’s are pollutions free, since the harmful substances are not used here.

There are some of the colors in LED like red, orange, blue, white, yellow and it can be easily controlled.

It can be used in many ways such as lights(collections of LED), Television, Mobile displays, watches, etc…

Disadvantages :

The cost of the LED’s are currently more expensive as it is calculated using lumen.

On seeing the total cost of the LED’s(including energy consumption and maintenance cost) and the other light emitters made up of halogen source, incandescent, the LED’s cost is high.

LED’s can shift their colors due to its age performance and temperature.

The correct voltage should be supplied to LED’s in a constant flow, if not then it gets failure.

 In some cases, the same color gets changed in characteristics which affects the color coding in a serial connections.

How to find the positive and negative terminal of a LED ?

There will be two terminals in LED. In that two, one of the terminals is bigger than the other. The bigger one is the positive terminal and the other one is negative terminal.

  

The unknown info about LED’s :

LED’s are used in a wide range of applications, because of its several characteristics in our day  today life. Some of the places where LED’s used , Traffic signals, Television, and many of the displays on our surroundings(shopping mall, shops, etc,..). There will not be any waste of energy in using LED’s. because it emits a light in a single direction on its way.

LED’s does not contains any harmful materials like mercury, fluorescent and it reduces the environment impacts while using LED’s. The usage of more LED’s reduces the carbon emission in the approximate range of 1800 millions metric tons. 

From the year of 2012, many Americans started to use LED’s by knowing the advantages of LED’s. approximately it saves $650 millions in their annual cost on energy.