LEDs

Kang BaeMaterial Science

MEEN 3344

What is LED LED stands for Light Emitting Diode. LED is a semiconductor device that produces

infrared lights when electric current is applied to the device

This process is also called Electroluminescense

HISTORY OF LED

Radio Corporation of America first reported on infrared emission from gallium arsenide in 1955.

Texas Instrument found Gallium Arsenide emits infrared lights when electric current were applied 1961.

GE developed the first working LED in 1962.

How LED works A LED is a semiconductor diode that consists of a

chip of semiconducting material that creates a p-n junction.

P-N junction is where current flows and it flows from the p-side to the n-side

Charge-carriers - electrons and electron holes - flow into the junction

releases energy in the form of a photon. The wavelength of the light emitted distinguishes

LED’s color Examples of colors aluminum gallium arsenide (AlGaAs) - red and infrared aluminum gallium phosphide (AlGaP) - green aluminum gallium indium phosphide (AlGaInP) - high-brightness

orange-red, orange, yellow, and green diamond (C) - ultraviolet

Uses of LED flash lights. LED Display Bicycle lights Traffic signs and

signals Mouse for

computers Cars (Lexus

tailamp)

Advantages and Disadvantage

Lasts longer than incandescent lights

Extremely durable and less heat Lights up in microseconds High ambient temperature cause

overheat. More efficient, lower power usage

than incandescent lights.

References Whatis June 18 2001, Nov 9 2006

http://whatis.techtarget.com/definition/0,,sid9_gci213613,00.html

Wikipedia Nov 9 2006, Nov 9 2006 http://en.wikipedia.org/wiki/LED_%28Light-emitting_diode%29#Physical_function