[Physics Class Notes] on Different Types of LED Pdf for Exam

LEDs are also known as light emitting diodes, it’s a semiconductor light emitting source that emits light when current is flown through it. Semiconductor electrons recombine with the electron holes releasing energy in the form of photons. Corresponding to the energy of photons the colour of light is determined, and also by the energy required by photons to cross the semiconductors band gap.  By using multiple semiconductors, white light is obtained or by a layer of light emitting phosphor on the semiconductor device.

The particle electronics components appeared in 1962. The earliest LED emitted low intensity infrared light in remote controlled circuits such as those used with a wide variety of consumer electronics.

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History of LED

A phenomenon known as electroluminescence was discovered in 1907, by the british experementor named H.J Round of marconi labs by using a crystal of silicon carbide and cat’s-whisker detector.

Oleg Losev, a Russian inventor, reported creation of the first LED in 1927. His research was distributed in Soviet, Germany, British scientific journals but no practical use was made of these discoveries for several decades.

Georges Destriau, in 1936 observed that electroluminescence could be produced with zinc sulphide power is suspended in an illustrator and an alternating electrical field is applied to it. In his distrial publication he often referred to luminescence as losev-lights.

He worked in the lab of madame Marie Curie, also an earlier pioneer in the field of luminance with research of radium.

Hungarian Zoltan Bay along with Gyorgy Szigeti, in Hungary pre attempted LED lightings in the year 1939 by pertaining a lightning device with an option on boron carbide, that emitted yellowish white, white or greenish white light depending on the impurities present.

Carl Accardo, Edward Jamgochain and Kurt Lehovec, explained these first LEDs in 1951 using an apparatus employing SiC crystals with a current source of a battery or a plus generator.

Types of LED

LEDs are made up of different packages and are used for different purposes.

These are mostly single die LEDs and they are available in various shapes and sizes from 2mm to 8mm through holes and the surface mount package. And the current rating ranges lie between 1mA to above 20mA. The multiple LED dies get attached to a flexible backing tape from an LED strip light. 

 These are the LEDs developed by the seoul semiconductor.  It can be operated             on AC power without a DC convertor. For each light cycle the LEDs part emits light which is dark. And this is reversed during the next half cycle. 

These high outputs or high power LEDs can be driven at currents from 100 of mA to more than an ampere. Some can emmite over thousands of lumen.

Overheating is proved to be destructive for the LEDs so the HP-LED can often replace an bulbe in a flashlight. It can be set in an array to form a powerful LED lamp.

Advantages and Disadvantages of LED

LEDs are used in many places here are some of the advantages of an LED:

• More lumens are emitted by LED per watt as compared to incandescent light bulbs. The LED lightning efficiency fixture is not affected by the size or shape, unlike fluorescent light bulbs or tubes.

• Colour LEDs can emit light of different colours without using any colour filter as the traditional lightning method needs. It can lower efficient costs, this is more efficient.

• Their size is adjustable from big to big and small to small. And are easily attached to the printed circuit board.

• LED lights up quickly, a red indicator light achieves full brightness light under a microsecond. At times the LED gives a faster response.

Disadvantages:

• The LEDs performance largely depends on the ambient temperature of the thermal management properties or the operating environment also.

• LEDs must be supplied with a voltage which is above their threshold voltage, and current below their rating.

• Area light source: the single LEDs do not approximate a point source of light which is giving a spherical light distribution.

Uses of LED

Uses of LEDs fall majorly under four categories that are:

In the visual signals where the light goes more or less directly from the source inside the human eyes, it does so to convey a message or meaning.

In illumination: where light is reflected from the objects to give visual responses. Interacting and measuring with the processes involving no human vision.

It’s also used in the narrow light sensor where LEDs operate in a reverse biased mode. And they respond to the incident light also instead of emitting light.

Due to their small size they can easily be fitted in anywhere and can be used time and again they are also available in many different shapes and sizes according to the users requirements.