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LED : Light Emitting Diode By , Prasanna.J

LED : Light Emitting Diode By , Prasanna.J. Light Emitting Diode: LED. Invented By :Nick Holonyak (1962). Applications of LED’s :. Your fancy mobile-phone, i-pod, TV and digital camera. LED as IR Sensor. What is an LED?. Light-emitting diode Semiconductor Has polarity

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LED : Light Emitting Diode By , Prasanna.J

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  1. LED : Light Emitting DiodeBy , Prasanna.J

  2. Light Emitting Diode: LED Invented By :Nick Holonyak (1962)

  3. Applications of LED’s :

  4. Your fancy mobile-phone, i-pod, TV and digital camera LED as IR Sensor

  5. What is an LED? • Light-emitting diode • Semiconductor • Has polarity • LED are semiconductor p-n junctions that under forward bias conditions can emit radiation by electroluminescence in the UV, visible or infrared regions of the electromagnetic spectrum. The quanta of light energy released is approximately proportional to the band gap of the semiconductor.

  6. Luminescence is the process behind light emission • Luminescence is a term used to describe the emission of radiation from a solid when the solid is supplied with some form of energy. • Electroluminescence  excitation results from the application of an electric field • In a p-n junction diode injection electroluminescence occurs resulting in light emission when the junction is forward biased

  7. Inside a Light Emitting Diode • Transparent Plastic Case • Terminal Pins • Diode

  8. Construction of Typical LED Al Light output p n Electrical contacts Substrate

  9. Electrical Contacts P-n junction How does an LED work’s (An Overview) :- # A typical LED needs a p-n junction # There are a lot of electrons and holes at the junction due to excitations # Electrons from n need to be injected to p to promote recombination # Junction is biased to produce even more e-h and to inject electrons from n to p for recombination to happen Recombination produces light!!

  10. LED: How It Works • When current flows across a diode • Negative electrons move one way and positive holes move the other way

  11. LED: How It Works • The holes exist at a lower energy level than the free electrons • Therefore when a free electrons falls it losses energy

  12. LED: How It Works • This energy is emitted in a form of a photon, which produces light • The color of the light is determined by the fall of the electron and hence energy level of the photon

  13. Colors And Materials :-

  14. Kinds of LEDs

  15. Miniature LED’s : Application Specific LED High Power LED

  16. How to Connect a LED: • Requires 1.5~3.3V and 20 mA • To prevent overloading, use resistor 470 Ω

  17. IV Characteristics : • In an LED, depending on the material used its cut in voltage can be anywhere between 1.5 to 3.3 Volts

  18. Basic advantages of LED Light : • Energy efficient - LED’s are now capable of outputting 135 lumens/watt • Long Lifetime - 50,000 hours or more if properly engineered • Rugged - LED’s are also called “Solid State Lighting (SSL) as they are made of solid material with no filament or tube or bulb to break • No warm-up period - LED’s light instantly – in nanoseconds • Not affected by cold temperatures - LED’s “like” low temperatures and will startup even in subzero weather • Directional - With LED’s you can direct the light where you want it, thus no light is wasted • Excellent Color Rendering - LED’s do not wash out colors like other light sources such as fluorescents, making them perfect for displays and retail applications • Environmentally friendly - LED’s contain no mercury or other hazardous substances • Controllable - LED’s can be controlled for brightness and color

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