LIGHT EMITTING DIODES

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LIGHT-EMITTING DIODES
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LEDs EVERYWHERE

• small electronics
• traffic lights
• vehicle signal lights
• jumbo stadium displays

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Not Just a Lightbulb

• no filament less heat
• illuminated by movement of electrons in
  semiconductor material

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Diodes

• simple semiconductor
• silicon with impurities
• N-type and P-type regions
• electrons and holes

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Charge Carrier Interaction
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Producing Light

• photons particle-like packets of light
• released from energy drop of electrons
• electrons combining with holes results in a drop
  to a lower orbital
• energy released is in form of photon
• greater-energy drop higher energy photon
  higher frequency light

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Different LEDs

• photons emmitted in all diodes
• standard Si diodes electrons drop a relatively
  short distance resultant electron is low
  freqency INFRARED
• visible light LEDs wider gap between conduction
  band and lower orbitals
• gap size determines light freqency color

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Where Does the Light Go?

• in ordinary Si diodes, the Si absorbs most of the
  light energy
• LEDs are specially constructed to release a large
  number of photons outward
• housed in a plastic bulb that concentrates the
  light in a particular direction

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See?
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Advantage, LED

• no filament to burn out
• more durable, smaller
• efficiency - little wasted heat

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Sources

• http//www.theledlight.com/pdf/technical.pdf
• http//www.howstuffworks.com