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MODULE 4: LEDs
SUMMER CHALLENGE
Electrical Engineering: Smart Lighting
Michael Rahaim, PhD Candidate
Multimedia Communications Lab
Boston University
[email protected]
Module 4: LEDs
07/11/2014
Overview
Boston
From
“Lighting”
to Here
Smart Lighting
University
Slideshow Title Goes
 What is a Diode?
 LEDs!
 Electrical Power
 LED Drivers
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Module 4: LEDs
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Lighting & Color Science
Boston
Visible
Light is a form of electromagnetic radiation
University Slideshow Title Goes Here
mm Wave Spectrum
100km
10km
1km
3kHz
30kHz 300kHz
100m
10m
1m
100mm
3MHz 30MHz 300MHz 3GHz
10mm
1mm
100μm
30GHz
300GHz 3THz
10μm
1μm
100nm
10nm
1nm
3PHz
30PHz
300PHz
30THz 300THz
microwave Spectrum
780nm
380THz
Visible Light Spectrum
400nm
750THz
 The human eye responds to the visible light spectrum
 White light is the presence of all colors
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Module 4: LEDs
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Smart Lighting
Boston
InUniversity
what Slideshow
waysTitle
can
light be better?
Goes Here
 Energy Efficiency
 Healthy Lighting
 Productivity (Data access)
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Module 4: LEDs
07/11/2014
What is a diode?
Boston
A University
device
that allows current to flow in one direction
Slideshow Title Goes Here
 Forward Bias Voltage
 For current to flow, diodes require a forward bias voltage
 In an ideal diode, voltage drop remains constant
Anode
Cathode
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Module 4: LEDs
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Kirchhoff’s Voltage Law
Boston
The
algebraic sum of all voltages in a loop must equal 0
University Slideshow Title Goes Here
I
+
R1
𝑉0 + −𝑉1 + −𝑉2 = 0
+
A
V0
V1
R2
V2
-
 Relationship to Diode circuits
 Once the diode reaches the turn on voltage, 𝑉𝑅 increases with 𝑉𝑆
 Current through the circuit increases with 𝑉𝑅
+ 𝑉𝐷  Decreasing 𝑅 also increases with 𝑉𝑅
+
𝑉𝑆 + −𝑉𝐷 + −𝑉𝑅 = 0
𝑉𝑆
- 𝑉𝑅 +
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Module 4: LEDs
07/11/2014
LEDs
Boston University Slideshow Title Goes Here
David Miller
Module 4: LEDs
07/11/2014
How Do LEDs Work?
Boston
LED
Materials
University Slideshow Title Goes Here
 Semiconducting materials
 Current can only flow in one direction
 Passing through the LED, electrons lose energy
 Lost energy creates photons
 Photons have discrete wavelength related to band-gap
 Band-gap width and energy
 The wider the band-gap, the greater the energy of the photon released
 Specialized materials & processes required to achieve wide band-gap
 Planck’s Relation:
E=
hc
l
Module 4: LEDs
07/11/2014
How Do LEDs Work?
Boston University Slideshow Title Goes Here
Materials
Science
Semiconduct
or Materials
Quantum Physics
Band-gap,
or Energy
lost by
Electrons
Energy of
Photons
Enineering Design Process
Physiology,
Neuroscience
Wavelength
(color) of
Light Emitted
Module 4: LEDs
07/11/2014
Small Band Gap: Low Energy Red Light
Boston University Slideshow Title Goes Here
Conduction Band
Small Band Gap
Valence Band
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Module 4: LEDs
07/11/2014
Large Band Gap: High Energy Blue Light
Boston University Slideshow Title Goes Here
Conduction Band
Large Band Gap
Valence Band
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Module 4: LEDs
07/11/2014
Typical LED Characteristics
Boston University Slideshow Title Goes Here
Semiconductor
Material
Wavelength
Colour
VF @ 20mA
GaAs
850-940nm
Infra-Red
1.2v
GaAsP
630-660nm
Red
1.8v
GaAsP
605-620nm
Amber
2.0v
GaAsP
585-595nm
Yellow
2.2v
AlGaP
550-570nm
Green
3.5v
InGaN
430-505nm
Blue, Violet, & UV
3.6v
Module 4: LEDs
07/11/2014
A (Brief) History of LEDs
Boston University Slideshow Title Goes Here
1968
LEDs on
handheld
calculators
1962
First
Infrared
LED
1962
First
Red
LED
1972
First
Yellow
LEDs
1971
First
Green
and
Blue
LEDs
1993
First High
Brightness
Blue LED
1976
LEDs
for
Fiber
Optic
Comm
s.
2006
First
White
LED
Module 4: LEDs
LED Applications: Signals and Indicators
Boston University Slideshow Title Goes Here
07/11/2014
Module 4: LEDs
07/11/2014
LED Applications: Lighting & Illumination
Boston University Slideshow Title Goes Here
Module 4: LEDs
07/11/2014
LED Applications: Sensing, Control, Moving Data
Boston University Slideshow Title Goes Here
Module 4: LEDs
LED Applications: Other
Boston University Slideshow Title Goes Here
07/11/2014
Module 4: LEDs
07/11/2014
Experiment I
Boston
LED
circuit
University Slideshow Title Goes Here
 Determining the turn-on voltage
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Module 4: LEDs
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Electrical Power
Boston
Power
is the rate that energy is consumed.
University Slideshow Title Goes Here
𝑃 = 𝑉𝐼
This is another one of those important equations…
 Power is measured in Watts [𝑊] or [J/s]
 Energy sources (such as batteries) produce power
while the load of the circuit absorbs power.
+ 𝑉𝐷 𝑉𝑆 − 𝑉𝐷
𝑉𝑅
=
𝐼=
𝑅
𝑅
+
𝑉𝑆
- 𝑉𝑅 +
𝑉𝐷 𝑉𝑆 − 𝑉𝐷
𝑃𝐷 = 𝑉𝐷 𝐼 =
𝑅
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Module 4: LEDs
07/11/2014
Electric Power
𝑉 = 𝐼𝑅
Boston
Combining
the previous equation with OHMS LAW:
University Slideshow Title Goes Here
2
𝑉2
𝑃 = 𝑉𝐼 = 𝐼 𝑅 =
𝑅
 Consider a 60𝑊 incandescent attached to a 120𝑉 source
 How does current change if you replace the 60W bulb with 120W bulb?
2
120
60 =
𝑅1
2
120
120 =
𝑅2
𝑅2 = 120 = 0.5𝑅1
𝑉
𝐼1 =
𝑅1
𝑉
𝑉
𝐼2 =
=
= 2𝐼1
𝑅2 0.5𝑅1
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Module 4: LEDs
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Experiment II
Boston
LED
Drivers
University Slideshow Title Goes Here
 Power Consumption
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Module 4: LEDs
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Recap
Boston
What
did you
University Slideshow Title Goes Here
today?
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