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Solid State Lighting for the Developing World (Summary Lecture) Loren Wyard-Scott 1 * & Dr. James Andrew Smith 2 * 1 Dept. of Electrical & Computer Engineering University of Alberta Alberta, Canada 2 Institute of Sports Science University of Jena Jena, Germany * Member, IEEE Outline • • • • • The Project’s Objectives Improving the Design Process Using Technology Closer to its Potential Knowing the Measurement Tools Conclusion The Project’s Objectives • 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 Bas-Ravine, Haiti The Project’s Objectives • Were these goals simple to meet? • Is your project a Success? A Failure? Do you have enough information to answer these questions? You are on the path to a solution, but there is still a lot of work to do! • Many of you may have found that the objectives are under-specified. For instance, how is charging performed? What sort of “work” will be done with this project as a light source? • Designing and evaluating often requires groups to work in “the grey”. Improving the Design Process • • Did you get lost on the way to finding a solution – in “the grey”? Finding a good solution to any real-world problem requires: 1. Understanding the problem – from many perspectives! (e.g. users, manufacturers) 2. Understanding what technology is available (always changing!): “Product Knowledge” 3. Understanding the principles of operation of the technologies used. Improving the Design Process • • Finding your way through any of these three items can be challenging. It gets simpler with experience (like this project)! Tools and protocols that can help: 1. Correlation matrices: Understanding Design Tradeoffs 2. Multi-discipline Design Teams 3. Critical Design Review 4. Putting the Project Through its Paces: Testing Design: Correlation Matrices • Real design problems always have tradeoffs. “Cheap, fast, good: pick two.” • To help understand the tradeoffs and how they will affect the outcome is important. • A tool that helps understand the tradeoffs is a “Correlation Matrix”. Design: Correlation Matrices Longer Brighter Battery Life Light Longer Battery Life Brighter Light Low Cost Low Cost --- -- (highly negative) (quite negative) -- Design: Multi-Discipline Design Teams • Almost every real-world project involves more than one field of technology. • Teams that have a wider set of experiences and knowledge to draw from are typically more successful. • Commonly required skill sets: electrical, mechanical, manufacturing, industrial design, technical writing, financial, resource management. Design: Critical Design Review • In practice it is not always possible to develop a team that has all skill sets covered. • A Critical Design Review (CDR) is a standard stage of project design that can help offset this lack. • Once a (usually paper-based) design is complete, the design is reviewed by people from all walks of life, including experts. • The feedback is used to improve the design, or, in some cases, terminates it: “go” or “no go”. Design: Testing • Testing a new product is a complicated process. • There are discipline- and technologyspecific courses and books dedicated to testing. • Companies that do nothing but this aspect of project development exist. • Ensure that the end-user has a chance to use a product candidate! Using Technology Closer to its Potential • Understanding the options that are at your disposal when designing is important: “Product Knowledge” gained from reading trade publications, journals, etc. • Your education provides you with the tools to understand how particular technology works. • Device datasheets are key to understanding the capabilities of a device. Technology: Datasheets Excerpt from the datasheet for Lite-On LTL-10223W, document BNS-OD-C131/A4 by Lite-On Electronics, Inc. Technology: Datasheets • This datasheet indicates that even though the LED can handle a maximum continuous current of only 30 mA, it can handle 120mA for 0.1 ms every 1 ms. • Is this relevant to our problem? Yes: it provides a way of providing more light with less power! Technology: Options We could turn on the LED very brightly with 120mA for a brief time, and take advantage of a human’s persistence of vision to remove the flicker! To create the time-varying voltage waveform requires some new knowledge – but it can be done! Technology: Options • In resistors, electrical power is dissipated as heat and results in a less power-efficient design. • We could minimize this power dissipation by a different circuit layout: • This requires the battery voltage to be high enough that both LEDs can be turned on. Technology: Options • Hopefully you found that using AA batteries results in an operating lifetime that far exceeds the required 2 hours. • This indicates that there may be the possibility of using something other than a battery to power the LEDs: super (ultra) capacitors! Technology: Options Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008. Technology: Options Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008. Technology: Options • Hopefully this has demonstrated to you that –Understanding what devices are available; and –Understanding how these devices operate both come into play during design. Knowing the Measurement Tools • It is always important to understand the capabilities and limitations of the test equipment and measurement processes. • Did you discover that using a CdS cell (in the manner we have) to measure illuminosity yields, at best, an approximate result? – Alignment-sensitive – Wavelength sensitive – Temperature sensitive • Understanding these bounds while constantly asking “is what we are observing consistent with what we know?” is important to any scientific process. Conclusion • Conventional, limited, sources of energy are being taxed more heavily as the world population increases. • As a result, environmentally- and energyconscious designs are now of paramount importance. • The system you developed here has taught you how some of the emerging technologies operate. Conclusion • You have learned a lot about the design process, and have hopefully enjoyed yourselves while doing so. • Successful completion of the project itself, Solid State Lighting for the Developing World, will see underprivileged peoples provided with a safe lighting system that can be used to expand their opportunities by improving productivity and literacy. 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 • Super Capacitors – http://en.wikipedia.org/wiki/Supercapacitor