Xiaoyu Sun
24012083
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 Intro
– what is led
 How does it works
 Where it uses
 Advantages and
disadvantages
 Green city
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Photo from
www.mulelighting.com
Photo from
www.gizmowatch.com
Photo Credit 2008-12-2
sandstep
via Flickr
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When current flows
across a diode,
negative electrons
move one way and
positive holes move
the other way.
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The holes are at
lower energy level
than the free
electrons, so when a
electron falls it loses
energy.
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The energy is
emitted in the form
of a light photon.
The wavelength
depends on the band
gap energy of the
materials forming
the p-n junction.
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Direct band
gap
Indirect band
gap
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
Indicators and signs

Lighting

Smart lighting

Non-visual applications
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Left: A supermarket in
Switzerland
Right: Parking garage in Raleigh,
NC
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
Smart lighting

Non-visual applications
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•
•
•
•
•
Efficiency
Color
Cost
Lifetime
On/Off time





Dimming
Cool light
Shock resistance
Focus
Toxicity
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
High price

Temperature dependence

Voltage sensitivity

Area light source
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
Raleigh, NC

Toronto, Canada

Ann Arbor, MI
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
Roughly estimation:
Assume
φ = 45 lm
I = 350 mA
V = 3.42 V
luminous efficacy
45 lm/(0.35 A x 3.42 V) = 38 lm/W
(From the website of U.S. department of energy)
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Category
Type
Overall
luminous
efficacy
Overall
luminous
efficiency
Incandescent
5 W tungsten
incandescent (120 V)
5
0.7%
40 W tungsten
incandescent (120 V)
12.6
1.9%
100 W tungsten
incandescent (220 V)
13.8
2.0%
100 W tungsten glass
halogen (220 V)
16.7
2.4%
100 W tungsten
incandescent (120 V)
16.8
2.5%
2.6 W tungsten glass
halogen (5.2 V)
19.2
2.8%
white LED
10-90
1.5% - 13%
white OLED
102
15%
Prototype LEDs
Up to 161
Up to 25%
Light-emitting diode
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Color
Wavelength (nm) Voltage (V)
Semi-conductor
Material
Infrared
λ > 760
ΔV < 1.9
GaAs, AlGaAs
Red
610 < λ < 760
1.63 < ΔV <
2.03
AlGaAs, GaAsP,
AlGaInP, GaP
Orange
590 < λ < 610
2.03 < ΔV <
2.10
GaAsP, AlGaInP,
GaP
Yellow
570 < λ < 590
2.10 < ΔV <
2.18
GaAsP, AlGaInP,
GaP
500 < λ < 570
InGaN / GaN,
2.18 < ΔV < 4.0 GaP,
AlGaInP, AlGaP
Green
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Color
Wavelength (nm) Voltage (V)
Semi-conductor
Material
Blue
450 < λ < 500
ZnSe, InGaN
2.48 < ΔV < 3.7 SiC/ Si as
substrate
Purple
multiple types
2.48 < ΔV < 3.7
Violet
400 < λ < 450
2.76 < ΔV < 4.0 InGaN
Ultraviolet
White
λ < 400
Broad spectrum
Blue w/red,
white w/ purple
3.1 < ΔV < 4.4
diamond (C),
AlN, AlGaN,
AlGaInN
ΔV = 3.5
Blue/UV diode
with yellow
phosphor
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Reference:
[1] S. S. Iyer 1, Y. -H. Xie. Science 2 April 1993: Vol. 260. no. 5104, pp. 40 – 46.
Light Emission from Silicon
[2] Nobuyoshi Koshida, Hideki Koyama. Efficient Visible Photoluminescence
from Porous Silicon.
[3] http://en.wikipedia.org
[4] http://electronics.howstuffworks.com
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