1. 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

2. Outline The Project’s Objectives Improving the Design Process Using Technology Closer to its Potential Knowing the Measurement Tools Conclusion

3. 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

4. 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”.

5. 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.

6. 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 Trade- offs 2.Multi-discipline Design Teams 3.Critical Design Review 4.Putting the Project Through its Paces: Testing

7. Design: Correlation Matrices Real design problems always have trade- offs. “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”.

8. Design: Correlation Matrices Longer Battery Life Brighter Light Low Cost Longer Battery Life --- (highly negative) -- (quite negative) Brighter Light -- Low Cost

9. 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.

10. 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”.

11. Design: Testing Testing a new product is a complicated process. There are discipline- and technology- specific 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!

12. 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.

13. Technology: Datasheets Excerpt from the datasheet for Lite-On LTL-10223W, document BNS-OD-C131/A4 by Lite-On Electronics, Inc.

14. 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!

15. 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!

16. Technology: Options This requires the battery voltage to be high enough that both LEDs can be turned on. 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:

17. 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!

18. Technology: Options Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.http://en.wikipedia.org/wiki/Supercapacitor

19. Technology: Options Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.http://en.wikipedia.org/wiki/Supercapacitor

20. 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.

21. 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.

22. Conclusion Conventional, limited, sources of energy are being taxed more heavily as the world population increases. As a result, environmentally- and energy- conscious designs are now of paramount importance. The system you developed here has taught you how some of the emerging technologies operate.

23. 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.

24. 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