LED Full Form

LED stands for Light Emitting Diode

LED is right now the most energy-efficient lighting technology available for use. The LED is a semiconductors light source. Mainly LED is a PN-Junction diode which emits light in direct current and uses electroluminescence to produce light. Electroluminescence is a process where diode converts electric current to light source by changing the state of electrons. LED is also known as solid state lighting (SSL). LED provide non-coherent, narrow-spectrum light when voltage is applied to it. the voltage must be forwarded voltage. 

LED follow a condition, the anode terminal should be put at a higher potential than cathode terminal as current flows from anode to cathode (positive to negative). LED accepts DC current. When a voltage is applied across the diode semiconductor then the Electrons and Holes are transferred to the P-N junction and produce energy then that energy is converted into light. 

LED has four main parts, that are semiconductor die, substrate, phosphor and lens. Mainly the LED provides white light but also can make many colors of light such as red, green, blue, yellow, etc. These colors are based on the chemical composition of the phosphor. 

Construction of LED

• The LED is packed in a clear or diffuse plastic or glass lens that provide a angular range of light distributions, like a Incandescent light Bulb.
• LED consist of a chip of semiconductor doped with impurities to create a P-N junction.
• The chips are mounted in a reflective tray in order to increase the light output.
• The contacts are made at the Cathode side by means of conductive adhesive and on the Anode side via gold wire to the lead frame.
• The plastic case encloses the chip area of the lead frame.

Circuit Diagram

History of LED

LEDs work on electroluminescence, the first natural experience of electroluminescence happened in the year 1907 by a British researcher Henry Joseph Round in Marconi lab. He was performing experiments on a crystal silicon carbide, also known as carborundum , in which he noticed that when a potential of 10 volts is applied to that crystal then it emits yellowish light. Then in between 1920 to 1927 a another researcher Oleg Vladimirovich Losev did experiments with electroluminescence who was a radio researcher of Russia. 
After this in the year 1955, another radio researcher of America Rubin Braunstein discovered that some simple diodes emit infrared light when connected to a direct current. Then in 1961 Gary Pittman and Robert Biard from Texas Instruments found that gallium-arsenide diode emits infrared light every time when it is connected to current and accidentally created an infrared LED, which is the first LED of world. But this infrared is not visible to human eyes. Then in 1962, Nick Holonyack worked for General Electric Company as engineer, invented the first visible light LED, which was a red colored LED made using gallium arsenide phosphide. 
Then many researches happened for the LEDs. And some more LEDs are invented, that are, 

1. In the year 1972, electrical engineer M. George Craford, invented the first yellow LED and a brighter red LED.
2. In the year 1976, Thomas P. Pearsall developed high brightness LED for use in optic fiber.
3. In the year 1979, Shuji Nakamura of Nichia Corporation invented first blue LED. 
   

Characteristics of LED

• Voltage : 1.5 to 3.5 volts
• Operating temperature : Normally its varies from to ,
• Frequency : 400 to 600 TeraHz
• Average power consumption :5 watt to 9 watt. Also 200 lm/W achieved in lab while testing.
• Opening Time : 100 ms
• Light Generated by LED is Directional
• 10 Degree increase of temperature will reduce 5% – 7% lumen output and if P-N Junction temperature is under 75 degree then it will enable the LED life for over 50, 000 hours.
• LED is operated in forward biased mode only
• The characteristics curve of the LED shows that the forward bias of 1 V is sufficient to increase the current exponentially. 
  

Advantages

• The main advantage of LED is, LEDs are Energy Efficient and Power consumption is very Low, LEDs Operate on very Low Voltage
• LEDs are emitting an extremely high level of brightness and the intensity of the light is very much higher than other lighting technology
• Heat produces from the LED is very less that other lights, such as incandescent bulb
• LEDs are emitted the energy, mainly that are in the visible spectrum, so the UV emission is not there in LED. So our eyes are not get effected.
• LEDs have great lifetime, average lifetime of a LED is 50000 Hour(5Years approx).
• LED can reveal the actual color of the light as compared to other lights, so the Color Rendering Index(CRI)of LED is great.
• LEDs are in very small size, so that anywhere we can fit a LED where its needed, So LED is a flexible and user friendly component.

Disadvantages

• LED performance largely depends on the limited temperature of the operating environment, if operating a LED in higher temperatures may result in overheating the LED and that will lead to device failure.
• Voltage supplied to the LED must be above the threshold and current below the rating, otherwise the LED might be damage. So the voltage sensitivity must be followed for LED.
• LED lighting is more expensive than the traditional light sources, such as Incandescent bulb
• LEDs can cause light pollution than other light sources because of Blue pollution. That is cool white LEDs emit proportionally more blue light than conventional outdoor light sources.
• LEDs do not produce a spherical distribution of light, so they are not advisable to use in open large area.
• The efficiency of LED decreases as the electric current increases.
• LED require the correct electric polarity to light-up, so a rectifier must be used to maintain the polarity.