C. T. Clarke, A. Sergejevs University of Bath, UK Acknowledgements

1. High intensity LEDs as a light source for repeatable and reproducible photo-catalytic experimentation: Challenges, Pitfalls and Opportunities • C. T. Clarke, A. Sergejevs • University of Bath, UK • Acknowledgements • The authors gratefully acknowledge the financial support of the European Commission under FP7 project 309846: • “Photocatalytic Materials for the Destruction of Recalcitrant Organic Industrial Waste – PCATDES”.

2. Superbright LEDs:What could possibly go wrong? • C. T. Clarke, A. Sergejevs • University of Bath, UK • Acknowledgements • The authors gratefully acknowledge the financial support of the European Commission under FP7 project 309846: • “Photocatalytic Materials for the Destruction of Recalcitrant Organic Industrial Waste – PCATDES”.

3. Motivation • Photo-catalytic experimentation requires light that is: • Repeatable • Reproducible • Controllable • Measurable • Uniform • Light Emitting Diodes seem to offer a convenient source for experimentation • What are the issues surrounding the use of LEDs for photo-catalytic experiments?

4. Challenges • Heat • Power out is as important as power in. • Failure • How will you know if one LED is not working? • Improvements • Loose Specifications can lead to unseen changes.

5. Heat • LEDs are relatively efficient • but there are wide variations • Power that is not output optically is output as heat • Heat produces changes in temperature that may impact: • Photo-catalysis • Sensors • LED • Component life • Image taken from: LED Engin LZ1-06U00 Datasheet

6. Failure • It may not be immediately apparent if a single LED in a group fails • Failure modes be: • Short / open circuit • Temporary / permanent • LEDs are usually current controlled • To detect most failure modes both LED current and voltage need to be monitored • Low current → open circuit • Low voltage → short circuit

7. Improvements • It is not safe to assume that LEDs will have a long and stable product life • Output may change significantly • Tighter specifications are more expensive • Part obsolescence is common • Images taken from: LED Engin LZ1-06U00 & LZ1-00UV00 Datasheets

8. Pitfalls • Dimming an LED • What you see is not what you get. • Maximum Brightness • How to get the most out of your LED

9. Pulse Width Modulation vs Dimming • Dimming of Lights is often achieved with Pulse Width Modulation • The eye cannot tell the difference if the modulation frequency is over 50Hz • Photo-catalytic reactions may respond differently to your eyes • Ultracapacitors are nowavailable for smoothing

10. Current input vs optical output • Applying maximum current to an LED can reduce it’s optical output due to temperature effects • The use of a heatsink or liquid cooling can help • The circuit board that the LED is mounted on is very important • Surface mounting is the best approach by far • Many LEDs are available pre-mounted on suitable boards • Image taken from: farnell.com

11. Current input vs optical output • Data for LED Engin LZ1-06U00

12. Opportunities • Packaging • Making changes can be easy • Calibration • Different but the same

13. Packaging • LED manufacturers often make multiple wavelengths available in the same package format • Having a visible light LED to swap in is great for testing • Multiple LEDs can beput in one package • Image taken from: LED Engin LZ1-06U00 Datasheet

14. Calibration • Calibration can be used to match output from LEDs with different efficiency levels • 400% variation is not unusual • Low cost memory devices can be used to keep the measurements with the device for automatic adjustment of output flux • Temperature of the LED circuit board is key factor and must be measured

15. Proposed System: Implementation

16. Conclusions • LEDs have many advantages for experimentation • But there are ways that they could skew your results • Careful design can allow systems to be created that give high quality results even where individual LED performance is variable