Gareth Jones of Enfis described the emergence of a “multi-watt” class of LED systems, which are finding use in medical light-based applications such as photo-dynamic therapy or skin treatments, as well as industrial applications (task lighting, UV curing) and in automotive sector. There are a wide range of design challenges and trade-offs in building such systems; for example, novel optical approaches are necessary to keep efficiency high while retaining compact size. Also, thermal management, involving conduction of heat away from the LED array coupled with convection (e.g. forced air cooling), involves consideration of cost, footprint and manufacturing complexity, as well as performance.
Andrew Dennington of Carclo Technical Plastics presented a series of optical design tips for luminaire designers. “Before you start,” he said, “consider where the luminaire will be used, find out if any regulations cover the product, and be realistic about the lumen output from your LEDs.” Because LED boards can get very hot, it’s important to select the right plastic material for the optics. Also, when defining the illumination requirements, it’s equally important to specify where you don’t want the light to go. Dennington also included a word of caution; “The latest generation of LEDs is not safe, and someone will have their eyes damaged by a high-power LED product,” he warned. “Check your products to the relevant standards.”
Vehicles and transport signalling
LEDs are widely used in road traffic signals, and have also been applied on rail networks. David Rudge of Westinghouse Rail Systems described how LEDs are now allowed as light sources in the specifications governing UK rail systems, which call for compliance between -20 and +40°C. “The colour variation with temperature of red and green LEDs can be accommodated within the spec,” said Rudge, “but the colour variation of yellow LEDs is a problem with existing technology.” Yellow LEDs drift by about 1 nm per 10C, or about 6 nm from -20 and +40°C, which is sufficient to move them outside the very narrow colour specification for yellow. An additional problem is the wide tolerance in LED bins of typically 4 nm, so that Westinghouse uses a secondary selection scheme, with another company making use of the unwanted LEDs.
Luc van der Poel of Philips Lighting described emerging applications for LEDs, explaining that new products are influenced by both technology and social and cultural trends. Solid-state lighting can readily be used to provide ambience, for example in a bathroom where the lighting required during the morning rush to get ready for work would be much different from that required for a warm relaxing atmosphere in the evening. The technology also provides design freedom, flexibility and impressive light effects, while being environmentally friendly due to the lack of mercury.
Wim Braber, Future Lighting Solutions, “The Complete Guide to LEDs”
Nic Houslip, Supertex Inc, “20 Ways to Drive LEDs”
James Stratford, Universal Science, “Thermal Management Issues in LED lighting”
Andrew Phillips, Forge Europa, “Practical Measurement of LEDs and Fixtures”
Bob Steele, Strategies Unlimited, “High-Brightness LED Market Review and Forecast”
Tim Holt, Institute of Photonics, “Applications of Novel Micro LED Technology”
Antoine de Ryckel, Barco, “LEDs in Large Displays”
Anthony Batt, Lumidrives, “Emergency Lighting”
Next year’s event
The 3rd international LED conference organized by Photonics Cluster (UK) will be held in the UK on May 16-17, 2006.