ABET Constraints and LED Chapter
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Transcript of ABET Constraints and LED Chapter
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Economical constraint
Less power
Long lifetime
Social constraint
High color rendering
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Health and safety constraints
No harmful excitation or materials
Sustainability constraint
Long maintenance periods
Environmental constraint
environmentally friendly
Less emission of carbon
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Light Emitting Diodes(LED)
Old technology (1970s)
Advanced from numeric displays andindicator lights to new potential
applications (e.g. exit signs, accentlights, task lights, traffic lights, cove
lighting, outdoor lighting and down
lighting)
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Three layers of semiconductor on substratei. P-type (when forward bias holes come from it)
ii. N-type (when forward bias electrons come from it)
iii. Active region (emits light when e + hole)
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The forward-bias and the reverse-bias properties of the pn
junction imply that it can be used as a diode.
negative charges (electrons) can easily flow through the
junction from n to p but not from p to n, and vise versa for holes.
When the pn junction is forward-biased, electric charge flows
freely due to reduced resistance of itWhen the pn junction is reverse-biased, the junction barrier
the resistance becomes greater and charge flow is minimal.
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In an incandescent lamp, a tungsten filament is heated
by electric current until it glows, emitting visible light.
In a fluorescent lamp, an electric current causes the gas
inside the tube to emit ultraviolet (UV) radiation, which
strikes the phosphor coating on the inside of the glass,
causing it to emit visible light.
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When current is applied, the negatively-charged electrons move toward
the positive side, and the positively-charged holes move toward thenegative side. At the junction, the electrons and holes combine. As this
occurs, energy is released in the form of light that is emitted by the
LED.
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Depending on the alloy used to make the
semiconductor, the light emitted by the LED can range
through the colors of the rainbow: red, orange, yellow,
green, and blue.
"White" light is created by combining the light from
red, green, and blue (RGB) LEDs, or by coating a blueLED with yellow phosphor.
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long lifetime:
More than 100,000 hours
Low power consumption:
80% >> light & 20% >> loss
Lower bill
More accurate color rendering: Provide clear objects color
Security
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Energy efficiency:
80 90%
Efficient lighting equipment:
Reflector & Refractor
Fewer electrical losses:
Dont require additional electronic
and electromagnetic components
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Instantaneous turn on and off:
Low-Voltage:
External solar energy source
Using remote
environmental friendly:
No harmful chemical ( e.g. mercury)
No filaments or toxic/combustible gases
lower CO2 emissions
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Low maintenance:
Long life time Operational in extremely cold or hot temperatures
operates well also in cold settings(-55 - 70C)
Dimming LED: Control the amount of lighting
Reduce the power consumption
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Expensive:
It made from an expensive material Lenses:
It doesnt produce a glow in all direction
Angle of radiation (40 70)