Brodrick offers SSL technology update

Jim Brodrick of the US DOE has given an update on SSL technology, highlighting areas where LEDs are succeeding and describing roadblocks to broader deployment.

In a session entitled "State of the industry and market forecast," Jim Brodrick, lighting program manager at the US Department of Energy (DOE), was the lead speaker at the LEDs 2011 conference in San Diego, CA. Brodrick described applications where LED-based solid-state lighting (SSL) is already succeeding as well as the technology shortcomings that are limiting the usage of LEDs in other applications.

Immediately Brodrick pinpointed the reason for the DOE's interest in SSL and investment in the technology. Quoting a DOE report issued earlier this year, Brodrick said that LEDs could yield 233 TWh in energy savings per year if LED lights totally replaced legacy sources in a short list of seven lighting applications – enough energy to power 19 million households.

Purpose-built luminaires

Brodrick made a general statement about midway through his presentation that summed up the state of the SSL industry. About LED lighting products, he said, "If you design from a clean sheet of paper, you can come up with products that are really very good." He added that good designs must address all aspects of a luminaire including LED chips, optics, electronics, thermal management, and mechanical design.

It's easy to see where Brodrick's statement applies in readily available products. LED-based tubes intended as replacements for linear fluorescent lamps are still struggling to match the incumbent technology. In contrast, Brodrick said that several LED-based integral luminaires that are designed to replace tube-based troffer fixtures – as opposed to just replacing the tubes - can match or exceed the performance of fluorescent technology.

In general, Brodrick said that SSL is doing extremely well in recessed downlights, outdoor area lights, 2x2-ft troffers (not tube based) and refrigerated-case lights. The technology isn't doing nearly so well in small retrofit lamps including A lamps, the aforementioned linear-replacement segment, and cove lighting especially in cases where the legacy luminaires utilize fluorescent tubes.

LED retrofit lamps

Brodrick spent more time discussing the problematic applications, acknowledging the continued interest in LED-based 4-ft tubes given the huge installed base of fluorescent troffers. He said the tubes are getting better and beginning to match the efficacy of fluorescents. But light output and distribution remain a problem as directional LEDs aren't a good match for fluorescent fixtures that were designed for a tube that radiates light around the entire cylinder.

Still, Brodrick said the LED tubes are beginning to work for some applications in terms of light output and cost. Specifically he said that the long life of LEDs make the tubes a fit for hard-to-reach applications. He also said the LED tubes are a good choice where vibration is present or in temperature extremes.

In the area of small replacement lamps including ubiquitous A lamps, Brodrick said that the technology is getting better although he said, "generally they don't match the output, color quality, and light distribution" of incandescent sources.

Brodrick described a recent DOE test of replacement lamps in which the agency visited eight big-box retail stores in the US and purchased 33 LED lamp products to test. He said that most failed to meet basic performance parameters that would satisfy consumers looking to replace incandescent or halogen lamps.

About the retailers, Brodrick said, "Some carry better products than others." The DOE hasn't identified the retailers in a publicly-available report, but Brodrick said the DOE had taken up the matter directly with the retailers to discuss the issue of consumer satisfaction with LED lamps.

Tackling roadblocks

Brodrick concluded by discussing some items that the SSL industry needs to address across the entire application landscape. He said that despite the finalization of the TM-21 standard to project LED life, the industry continues to struggle to differentiate between lumen depreciation and luminaire life. We covered that very topic in the article " Understanding the difference between LED rated life and lumen-maintenance life" published in the October 2011 issue of LEDs Magazine. The DOE is working on the problem in conjunction with the Next Generation Lighting Industry Alliance and has published a paper focused on LED luminaire lifetime and reporting.

In terms of color quality, Brodrick said that the LED makers have made significant improvements and that tighter binning is a great benefit to luminaire makers. But he also said, "Color shifts over time are not well understood or predictable." He suggested more research is needed on the topic.

Brighter LEDs are also desirable of course. The DOE continues to raise lumen output and efficacy goals in its SSL Multi-Year Program Plan. In terms of efficacy, Brodrick said, "We're going for 258 lm/W." That's the goal for cool-white LEDs by 2020. For comparison, incandescent lamps are around 12 lm/W.

Tradeoffs were the final topic. In these relatively early days of the LED lighting industry, many conference talks have focused on optimizing every element of a luminaire including light output, color quality, efficacy, adaptive controls, and serviceability. Brodrick expects more affordable products to emerge as industry players identify what tradeoffs to make in specific applications.

Brodrick provided one example in the choice between modular-based approaches and what he calls an integrated luminaire that is purpose built for a single application. He said integrated luminaires typically have fewer components and lower assembly costs. He said modular designs are more convenient and can even be user serviceable but will also generally cost more.

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