Download Background Lecture - IEEE Real World Engineering Projects

Solid State Lighting for the
Developing World
Loren Wyard-Scott 1 *
&
Dr. James Andrew Smith 2 *
1
Dept. of Dept.
Electrical
& Computer
Engineering
of Electrical
& Computer
Engg
University
of Alberta
University
of Calgary
Alberta, Calgary,
Canada Canada
2
Institute Institute
of SportsofScience
Sports Science
University
of Jena of Jena
University
Jena, Germany
Jena, Germany
*
Member,Member,
IEEE IEEE
Introduction:
Why Are Lights Important?
• Productivity
– Longer work days
– Indoor working conditions
• Literacy
– Schoolwork is possible even in the
evening
• Safety
– You can see where you are walking &
driving
Lighting in the
Developed World
• Minority of world population
• Use a majority of energy resources
• Lighting is abundant & taken for granted
• Pollution
problems
caused by
associated
power systems.
Earth at night. Where are the developed nations?
Lighting in the
Developing World
• Majority of the world’s population
• 2 billion people without modern lighting
• Current Solutions
– Nothing
– Kerosene lamps
– Candles
• Dangers
– Fires
– Carbon Monoxide
– Sulpher Dioxide
Voting by candlelight in Haiti
Challenges for Modern
Lighting in Developing World
• Limited electricity supply
– Often no electrical grid
– Micro energy sources (diesel, solar, hydro)
• Difficult operating conditions
– Temperature ranges
– High humidity
– Dust and dirt
• Limited replacement parts
– Limited distribution infrastructure
– Sustainability: require local businesses
Benefits of LED lights
•
•
•
•
LED: Light Emitting Diode
Solid-state devices, like transistors
LEDs use less energy than regular incandescent bulbs.
They’re safer, more durable & cost less
Lamp
Homemade Incandescent
Compact
Type
Kerosene
Fluorescent
Efficiency
[Lumens/
0.03
5 - 18
30 - 79
Watt]
Rated Life
Supply of
6500 [Hours]
1000
Kerosene
Durability
Cost after
50,000
Hours [$]
15,000
White
LED
25 - 50
50,000
Fragile &
Dangerous
Fragile
Fragile
Durable
1250
175
75
20
Engineering
Development Process
1.
Identification of problem
–
–
2.
What is possible?
Keep it simple & effective!
Risk evaluation
–
5.
6.
7.
8.
Prototype
What actuators and sensors? At what cost?
Determine level of functional replacement
–
–
4.
What function is missing?
Talk to the clients!
Identification of affordable technology
–
3.
Start
Never underestimate what can go wrong!
Prototype device, test & start again (Steps 1 -5)
Test on larger population set
International certification
Manufacture & distribute device

Test

Manufacture
End
Rapid Prototyping
• “Express - Test - Cycle” approach to design
–
–
–
–
–
–
Identify a need & design objectives
Brainstorm for solutions
Express an idea in a physical device
Test the device
Discover problems that you weren’t aware of
Repeat until you’ve met the design objectives
• Rapid prototyping systems
– Combine modular, off-the-shelf components
– Great for quick mock-ups & functional testing
– Examples
• Breadboards
• Vector board
• Speed Wire
Breadboard system
The Project Structure
• Knowledge about key topics will help you succeed
• Introduction to basic electrical theory
– Ohm’s Law
– Battery operation
– Diode operation
• Introduction to basic light theory
– Light intensity (illuminance)
– How the eye filters different types of light
• Measurement procedures
– How to measure light with photoresistors
• Packaging for the real world
Background on Light:
Photometry
• Radiometry
– Science of measuring radiant energy
– Includes light, radio, x-rays, etc.
– In terms of absolute power
• Photometry
– Science of measuring light
– With respect to perceived intensity in the human eye
Light Measures, Part 1
• Luminous Flux
– A Photometric measure
– The “perceived” power of light with respect to the
human eye
– Unit: Lumen (lm)
• Luminous flux by a light source that emits one candela of
luminous intensity over a solid angle of one steradian
– Equivalent Radiometric (absolute) measure:
• Radiant Flux
Light Measures, Part 2
• Illuminance
– Measure of light intensity
– Used to measure light that hits a surface
– Units: Lux
Luminous Flux  Lumens 
Lux  

 Incident Area  meter 2 
• Luminous Emittance

– Light intensity emitted at a light source
– Units are also in Lux
Measuring Illuminance
• Device: Light Meter
– “Lux Meter”
– Report Illuminance
– Units: Lux
• Found in cameras
– Contain photodiode,
photoresistor, etc.
Illuminance vs. Distance
• Light intensity decreases with distance
• Fewer photons hit the same surface area with
increasing distance
• Inverse Square Law
2
2
I1  d1  I2  d2
– Intensity, I1, at distance d1
– Intensity, I2, at distance d2
• Only valid for point source!
– LED light patterns are complex
The Light Spectrum
• The human eye is sensitive to
certain wavelengths of light.
– Each wavelength is a different
colour
– White light is all colours!
Colour vs. Wavelength
400nm
750nm
• Human eye: 400 - 750
nanometers [nm]
– We can see blue, green, red
– We cannot see infrared (~900 nm)
• But video cameras ARE sensitive
to infrared
• Hold your remote control to a
video camera and test it yourself
Infrared LED light from
a remote control
Human Eye
• The eye filters out certain types of light
• Sensitive to a range of wavelengths
– 400 to 750 nm
• Above 750nm: invisible infrared
• Below 400nm: invisible ultraviolet (UV)
Visible!
Light Source Spectrum vs.
Sensor Spectral Response
• Your light source produces human-visible light
• Your light sensor (for testing) should emulate human
eye sensitivity
• It’s a weighted average: higher weight @ 600 nm
– More light needed @ 700 nm to get same sensor response
Electricity Background
• It’s the movement of electrons.
• Batteries store electrons
– Voltage [Volts]
• Wires let electrons travel
– Current [Amperes]
• Resistors convert electrons to heat
– Resistance [Ohms]
Voltage & Batteries:
Series & Parallel
• Batteries are made of individual cells
• Series cells: more voltage
• Parallel cells: same voltage, longer life
Single Cell
Series Cells
Series & Parallel Cells
Resistors in Series & Parallel
• Resistors resist
current flow.
• Resistors in series
– add up
Series Resistance
• Resistors in parallel
R
1
1
1

R1 R 2
Parallel Resistance
Ohm’s Law
• Relates the main
electrical elements.
• I=V/R
– Battery has constant
voltage [V]
– Current [I] varies
with resistance [R]
– Larger resistance
means smaller
current
Voltage Drops
• Batteries increase circuit voltage
• Resistors & other devices “drop” voltage
– Sum of “drops” equals battery voltage
• Imagine walking on a mountain.
– Battery raises you to the top
– Resistors, etc. drop you down.
Electrical Power
• Power (P) is measured in Watts
• Multiply current (I) by voltage (V)
– Current flowing through the circuit
– Voltage across the circuit
P  IV
Kirchoff’s Current Law
• Complicated circuits have many branches
– Especially parallel circuits!
• Current flow has into a branching path
– Equals sum of currents in the branches
• Useful for circuits with parallel LEDs, etc.
Ia  Ib  Ic  Id
The Diode
• A semiconductor device
• Current flows in one direction only.
• The diode’s PN junction controls
current flow
• Anode & Cathode on either side of
the junction
Anode
• If Anode has a more positive
voltage than the Cathode, it is
“forward biased”
– Lets current through
• Otherwise it’s “reverse biased”
– Won’t let current through
Cathode
Model #1: The Corner
• A “model” is a simplified imaginary version of
the actual device
• Apply a low voltage
– It stays off
– No electrons go through
– Current is zero
• Apply a high voltage
– It turns on!
– Electrons pass through
– Current is allowed
• Voltage drop across diode is constant: Vd
Model #2: The Square Law
• The “Square Law” model
is more realistic than the
“Corner” model
– But is more complicated
– I = a*V2
– The diode “switch” turns
on quickly in the “Corner”
model.
– The diode “switch” turns
on slowly in the “Square
Law”
• Voltage drop across diode is not constant
Diode Operation
• Goal: determine current
• Battery voltage: 3V
• Diode Vd: 0.7V
• The “Turn on” voltage
• Assume constant (Corner model)
• 200 Ω Resistor Voltage:
• 3 - 0.7 = 2.3 V
• I=V/R
• 2.3 / 200 = 0.01 A
• Current is 0.01A
Light Emitting Diode
(LED)
• Light Emitting Diode
(LED)
• Operates like a
regular diode
• The lens lets
photons out
– Converts electrons to
photons
• Higher current
– Brighter light!
LED Operation
• Operates like a diode
• Control brightness
• Change resistance
• Vf depends on LED
• 1V to 3V
• If battery is low the
LED won’t turn on
Reading LED Datasheets
Key features to look for:
– Vf: typical and maximum voltage drops
– Iv (mcd): luminous intensity in millicandelas for 20
milliamperes of current
• 1 candela = 1 lumen / steradian
– : wavelength (colour)
– Maximum forward current
CdS Photoresistor
Photoresistor Resistance vs Illuminance
(Advanced Photonix PDV-P9002-1)
Light Intensity (Lux)
• Light sensitive sensor
• CdS = Cadmium Sulfide
• Input light level
changes output
resistance
100
y = 3E+08x -1.789
10
– Brighter light = lower
1
resistance
1,000
– Softer light = higher
• Spectral
Response
resistance
– Best between 400 and 800 nm
– Approximates human eye response
10,000
Resistance (Ohms)
100,000
Photoresistors, continued
• Typically used as a light sensor
– Indoor night lights
– Outdoor street lamps
• Alternatives
– Generally more complex than photoresistor
– Solar cells
– Photodiodes
• Unlike LED, it receives light instead of transmitting it
• Used in light meters
– Phototransistors
• Often used in optical isolators
• Used to separate two electrical circuits for safety
Measuring Relative Light
Intensity
• Experimental Setup
– LED
– CdS Photo-resistor
• Light-sensitive
• Variable resistance
• Increase LED
current
LED Current vs. CdS Resistance
350
CdS
Resistance
– Brighter light
– Decrease in CdS
resistance
300
250
200
150
100
50
0
0.00
10.00
20.00
LED Current (mA)
30.00
40.00
Battery Life
• Battery life
– Inversely proportional to current
– Use resistance to control current
• Low current operation
– Higher resistance
– Lower current
– Weaker light & longer life
• High current operation
– Lower resistance
– Higher current
– Brighter light & shorter life
Final Project:
Scenario & Goals
• Scenario
– A remote village of 500 people
– Limited access to light at night
– Solar charger during the day
• Objective
– Build a portable LED lamp
– Easy to recharge
– Two hours of usage
– For work & reading
• Keep in mind:
–
–
–
–
Bas-Ravine, Haiti
Target group for the final design
What socio-economic factors affect engineering projects?
Where will the device be used?
How will the target group use the device?
Packaging for the Real World
•
KISS: “Keep it Simple, Stupid!”
– Simpler designs have less flaws
– Murphy’s Law: “If it can go wrong, it probably will.”
•
Intuitive usage
– Nobody reads the manuals
– Must be easy to recharge & operate!
•
Rugged design
– Can you drop it without breaking it?
•
Design for the local environmental conditions
– Dust, sand, snow, humidity, etc.
For more information
• Light Up The World (LUTW)
– http://www.lutw.org/
• Hyperphysics:
– http://hyperphysics.phy-astr.gsu.edu/hbase/vision/photomcon.html
• Dr. Dr. Bill’s Optics Stuff
– http://drdrbill.com