1. Solid State Lighting for the Developing World Loren Wyard-Scott 1 * & Dr. James Andrew Smith 2 * 1 Dept. of Electrical & Computer Engg University of Calgary Calgary, Canada 2 Institute of Sports Science University of Jena Jena, Germany * Member, IEEE Dept. of Electrical & Computer Engineering University of Alberta Alberta, Canada Institute of Sports Science University of Jena Jena, Germany Member, IEEE

2. 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

3. Lighting in the Developed World Minority of world population Use a majority of energy resources Lighting is abundant & taken for granted Earth at night. Where are the developed nations? Pollution problems caused by associated power systems.

4. 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 –Sulphur Dioxide Voting by candlelight in Haiti

5. 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

6. 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

7. Engineering Development Process 1.Identification of problem –What function is missing? –Talk to the clients! 2.Identification of affordable technology –What actuators and sensors? At what cost? 3.Determine level of functional replacement –What is possible? –Keep it simple & effective! 4.Risk evaluation –Never underestimate what can go wrong! 5.Prototype device, test & start again (Steps 1 -5) 6.Test on larger population set 7.International certification 8.Manufacture & distribute device Start End Manufacture Prototype Test  

8. 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

9. 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

10. 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

11. 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

12. Light Measures, Part 2 Illuminance –Measure of light intensity –Used to measure light that hits a surface –Units: Lux Luminous Emittance –Light intensity emitted at a light source –Units are also in Lux

13. Measuring Illuminance Device: Light Meter –“Lux Meter” –Report Illuminance –Units: Lux Found in cameras –Contain photodiode, photoresistor, etc.

14. Illuminance vs. Distance Light intensity decreases with distance Fewer photons hit the same surface area with increasing distance Inverse Square Law –Intensity, I 1, at distance d 1 –Intensity, I 2, at distance d 2 Only valid for point source! –LED light patterns are complex

15. The Light Spectrum The human eye is sensitive to certain wavelengths of light. –Each wavelength is a different colour –White light is all colours! 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 Colour vs. Wavelength Infrared LED light from a remote control 750nm400nm Invisible infrared

16. 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) invisible Visible!

17. 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

18. 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]

19. Voltage & Batteries: Series & Parallel Batteries are made of individual cells Series cells: more voltage Parallel cells: same voltage, longer life Single CellSeries CellsSeries & Parallel Cells

20. Resistors in Series & Parallel Resistors resist current flow. Resistors in series – add up Resistors in parallel Series Resistance Parallel Resistance

21. 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

22. 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.

23. Electrical Power Power ( P ) is measured in Watts Multiply current ( I ) by voltage ( V ) –Current flowing through the circuit –Voltage across the circuit

24. 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.

25. 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 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 AnodeCathode

26. 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: V d

27. Model #2: The Square Law The “Square Law” model is more realistic than the “Corner” model –But is more complicated –I = a*V 2 –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

28. Diode Operation Goal: determine current Battery voltage : 3V Diode V d : 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

29. Light Emitting Diode (LED) Operates like a regular diode The lens lets photons out –Converts electrons to photons Higher current –Brighter light!

30. LED Operation Operates like a diode Control brightness Change resistance V d is typically referred to as V f or V fwd (forward voltage drop) when talking about LEDs V f depends on LED 1V to 3V If battery is low the LED won’t turn on

31. Reading LED Datasheets Key features to look for: –V f : typical and maximum voltage drops –I v (mcd): luminous intensity in millicandelas for 20 milliamperes of current 1 candela = 1 lumen / steradian – : wavelength (colour) –Maximum forward current (these models can handle 30mA max)

32. CdS Photoresistor Light sensitive sensor CdS = Cadmium Sulfide Input light level changes output resistance –Brighter light = lower resistance –Softer light = higher resistance Spectral Response –Best between 400 and 800 nm –Approximates human eye response

33. 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

34. Measuring Relative Light Intensity Experimental Setup –LED –CdS Photo-resistor Light-sensitive Variable resistance Increase LED current –Brighter light –Decrease in CdS resistance

35. 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

36. 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: –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? Bas-Ravine, Haiti

37. 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.

38. 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