ABET Constraints and LED Chapter

8/13/2019 ABET Constraints and LED Chapter

1/13

Economical constraint

Less power

Long lifetime

Social constraint

High color rendering


2/13

Health and safety constraints

No harmful excitation or materials

Sustainability constraint

Long maintenance periods

Environmental constraint

environmentally friendly

Less emission of carbon


3/13

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)


4/13

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)


5/13

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.


6/13

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.


7/13

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.


8/13

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.


9/13

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


10/13

Energy efficiency:

80 90%

Efficient lighting equipment:

Reflector & Refractor

Fewer electrical losses:

Dont require additional electronic

and electromagnetic components


11/13

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


12/13

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


13/13

Expensive:

It made from an expensive material Lenses:

It doesnt produce a glow in all direction

Angle of radiation (40 70)

ABET Constraints and LED Chapter

Documents