1. LED : Light Emitting Diode By , 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
Light output p n
Electrical contacts
Substrate

9. Recombination produces light!!
P-n junction
Electrical Contacts
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