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Lighting Community Outlines Challenges For LED Industry

Lighting designers are eager to increase their adoption of LED technology, but are looking for device suppliers to remove some of the hurdles, writes Tim Whitaker.
While LED manufacturers concentrate on improving the brightness and efficacy of their devices, many designers and specifiers in the lighting community remain unsure of how to adopt this new technology in their products and projects. This discontinuity was highlighted at the "LEDs: Meeting the Design and Performance Challenges" conference, which was held in London, UK, in late January. Organized by Lighting Equipment News magazine and the UK-based Lighting Industry Federation, the one-day event was slanted more towards end-users in the lighting industry than device manufacturers, although speakers from Lumileds and Osram Opto Semiconductors represented the latter group.

Challenges and benefitsAlthough there are many benefits associated with using LEDs for lighting applications, there are also many issues to resolve. Factors such as cost and luminous efficacy, and the lumens per dollar figure-of-merit, are always mentioned at LED conferences, but other factors can be equally important to lighting designers. These include standards, lifetime and reliability, color variations over time and from batch to batch, what types of fixtures to use with LEDs... the list goes on.

Take lifetime, which is routinely quoted as one of the main benefits of using LEDs. Lifetimes of 100,000 h (more than 11 years) are often mentioned, which effectively means that the LED is unlikely to fail, unlike an incandescent lamp. However, in reality, the lumen output of an LED degrades over time, to an extent determined by many factors including its color, the operating conditions and the manufacturer. As pointed out by Jonathan David, secretary of the Society of Light and Lighting, the effect of this lumen depreciation depends on the application. "It can be relatively unimportant for decorative lighting, where the changes go largely unnoticed, but very important for task lighting," he said.

At present, there is no standard definition of lifetime. Keith Scott, market development manager with Lumileds, says that his company specifies its white and colored Luxeon LEDs as having an average lumen maintenance of 70% (i.e. the lumen output drops by 30%) at 50,000 h. This is a useful starting point, although this level of degradation is unsuitable for some applications. (It should be pointed out that other light sources also experience lumen degradation.) Conversely, some applications simply don t require such long lifetimes.

Carsten Schaffarz, manager of product management and marketing with Vossloh-Schwabe, identified the lack of standardization in the LED industry as a problem for companies trying to evaluate the cost benefit of using LEDs rather than other light sources. "There are few standards, and performance varies from one manufacturer to another," he said. "The cost benefit is difficult to define and it is down to the end-user to undertake the final evaluation." LEDs will only be used to replace existing light sources if the advantages are clear and if higher costs are justifiable.

Fortunately, acceptable benefits can be psychological as well as economic, especially in Europe, where in general more value is placed on light quality. An example was given by Alan Oliver, sales and marketing director for Telectra, a company that has installed lighting systems in aircraft for airlines including Virgin Atlantic and KLM. The principal advantages of LED-based lights in this application are ease of maintenance, safety, and the ability to adjust the appearance of the light (for example color and intensity) to maximize passenger comfort.

Metrics and standardsKevin Dowling, vice-president of strategy and technology at the specialist LED lighting company Color Kinetics, described a metric for comparing the relative costs of different lighting technologies. The "cost of light" metric encompasses not only the cost of the light source and fixtures, but also the cost of maintenance and electricity over the lifetime of the light source. Although incandescent lamps have a very low cost and high lumen output compared with LEDs, the LED source has a much longer lifetime and consumes far less power. In fact, typical LEDs already have a lower "cost of light" than incandescent and halogen sources, according to Dowling, although this is not widely appreciated. "Most Color Kinetics installations are not driven by energy savings, although the benefits are still there," he said.

Speakers and panelists kept returning to the issue of standards. Richard Hall of Thorn Lighting commented: "There is a very high need for standardization to allow luminaire [lighting fixture] manufacturers to manage their customers expectations." In fact, a number of standards are being developed by the CIE, the International Commission on Illumination, relating to areas such as the measurement of LED flux, color rendering index, and other properties. In some respects, LEDs will need to fit in with existing standards. "There are a number of internationally recognized standards, for example covering transport-related lighting applications, and LEDs will have to adapt themselves to fit around these," said Jonathan David. With regard to photobiological safety, Telectra s Oliver pointed out that the regulations covering laser eye safety also cover LEDs.

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