INDUSTRY

of Energy (DoE) roadmap compiled inconjunction with a panel of industry experts,current white-light LEDs can produce from 20 to45 lm with a luminous efficiency of 20 lm/W or45 lm/W, respectively. In contrast, a typicalfluorescent bulb produces 5300 lm at a luminousefficiency of 83 lm/W, and a high-intensitydischarge bulb produces 24 klm at a luminousefficiency of 80 lm/W. Clearly, LEDs are at anenormous disadvantage in terms of overall output,despite boasting lifetimes a factor of two or morehigher than the other technologies.

Industry doesn’t care as much about lifetime ifit can’t get the light it needs for an assembly lineor a high bay, though. “For these particularapplications, I think the requirement is still tensof thousands of lumens,” says Srinath Aanegola,director for white LED technology atGELcore (Valley View, OH), and amember of the technicalcommittee for the DoEreport. “Whether solid-state lighting will bethe right choice isstill a questionmark.”

Solid-state lighting faces challenges, opportunitiesin industrial applications.

By Kristin Lewotsky

SPIE Professional July 200612

LLighting is poised to be the next great solid-statefrontier. The technology is already making inroadsin the markets for architectural lighting, signage,and specialty residential and retail applications.

According to Robert Steele, director ofoptoelectronics programs at Strategies Unlimited(Mountain View, CA), the overall lighting marketfor LEDs in 2005 was an estimated $250 million.Hard numbers aren’t yet available, but he projectsthe market to reach roughly $1 billion by 2010,with steady year-over-year growth rates of 30 to 40%annually. “It’s still small but it’s emerging,” he says.“There’s a huge amount of activity.”

One of the strengths of LED lighting isreliability, making the industrial market a naturaltarget of opportunity. In an industrial setting,replacing burned out bulbs doesn’t just incur partscosts but also production downtime costs. Giventhe industrial setting’s voracious appetite forlumens, however, LED lighting is going to haveto meet some pretty strict performance standards.

Industrial StrengthLEDs generate white light through a mix of red,green, and blue output or by downconversion viaphosphors. In theory, the technology offers highefficiency; the reality is lagging a bit.

According to “Solid-State Lighting Researchand Development Portfolio,” a U.S. Department

Power OnOf course, the aforementioned DoE roadmapcarries two important milestones: reaching anefficiency of better than 100 lm/W by 2010 andreaching a value of $3/klm by 2015 (compared to$0.6/klm for fluorescents). Companies like Nichia(Tokyo, Japan) have reported reaching 100 lm/W for small white-light LEDs, but efficienciestypically drop by 50% when devices are scaled upto the large chips and color temperaturesappropriate for industrial applications.

Past the magic 100 lm/W barrier, a whole hostof interesting things happen. LEDs will providebetter luminous efficiency and lifetime than anylighting alternative, on a competitive cost basis.

“In an industrial or a commercial setting, peoplepay attention to life cycle costs,” says Steele. “Ifyou’re saving on labor and savingon electricity, you’re willing topay more up front.”

With this efficiency comesthe opportunity to achievehigh-lumen output. Consider awhite-light LED that produces1000 lm at 100 lm/W.“Because I have moreefficiency, can I drive itat 30 W and get threetimes the light output,make this a 3 klm source?” Aanegola asks. “I thinkthat’s what most people will try to do because whatis going to drive penetration is how many lumensyou’re getting for every dollar you spend.”

Of course, this approach raises the pesky issueof thermal management. Incandescent andfluorescent bulbs dissipate heat radiatively; LEDsare limited to conduction and convection.Moreover, incandescents generate and releasemost of their heat through the front of the bulb,which is available to the open air; LEDs generatemost of their heat at the back, where they wouldpresumably be plugged into a fixture. When you’retalking about 4 or 5 W, it’s not such a challenge.When you’re talking about dissipating the tensor even hundreds of watts that could be generatedby an industrial fixture, however, conductive andconvective cooling are simply not feasible. Notonly are there safety issues, there’s the nasty littlefact that elevated heat slashes device lifetime,which is a key part of the LED lighting valueproposition.

“Then you’ve got to maybe change the shape,the fixture, and include active cooling techniquesso you’re not impacting lifetime, which is a keyrequirement,” says Aanegola. But he’s quick topoint out that adding a thermoelectric cooler ora fan, say, in turn adds cost or failure points.

In the case of office lighting, for example, whichwould face far lower output requirements, cooling viaheatsinks presents less of a challenge, says Kathryn

Lighting Upthe FutureIf what Kathryn Conway,principal of LED Consulting(Nassau, NY) saw at theLight+Building show(Frankfurt, Germany; 23–27April) is anything to go by,the future looks bright forsolid-state lighting ingeneral. “What’s reallyobvious is that every majormanufacturer feels theobligation to show someLED products,” she says.The show had more than300 exhibitors from aroundthe globe in the area ofLED lighting.

Of course, true marketpenetration by LEDs hasalways hovered somewherein the tantalizingly closefuture. That may bechanging, according toConway. “For years, peoplehave been saying in five to10 years we’ll see LEDs,five to 10 years, but I thinkthis is the year we’ll markas the beginning of the realadoption of white LEDs,”she says. In part, shepoints to the critical massof manufacturers nowparticipating in the sectorthrough technologylicensing. R&D effortsdriven by demand in thedisplay and automotiveindustries have alsoprovided a push.

Don’t look for LEDs to be atyour local hardware storetomorrow, but for anincreasing number of nicheapplications, white-lightLEDs make sense, forexample in cove lightingand certain types of retaillighting.

In addition, manufacturerssuch as Color Kinetics areshowing white-light LEDsthat can be adjusted incolor tone from warm whiteto cool white. Applicationsinclude retail, high-endresidential and even enter-tainment venues such asmuseums. “Last year theyhad prototypes,” she says.“This year, they’re real.”

—K.L.

July 2006 SPIE Professional 13

Conway, LED Consulting (Nassau, NY). “Because theyhave to have a lot of surface area, they can be made indecorative shapes so it doesn’t really detract. It can bemade kind of aesthetically pleasing.”

Fitting the NicheIf LED lighting for general industrial illuminationhas yet to take off, the technology is still movingalong one niche at a time. “You have to find whereLEDs will bring some value that you can’t get withother light sources,” Steele says. LED reliability, forexample, has gained the technology a strongfoothold in machine vision. “If the lamp on yourmachine vision system fails and you’ve got to shutthe production line down for even 10 minutes tochange it, that could be thousands of dollars of lostproduction time.”

Conway recently scouted the Light+Buildingshow (Frankfurt, Germany; 23–27April) and discovered new trends inindustrial lighting, including office-type fixtures that feature LEDs on theedges, mixing their output with thatof other sources. “They’re using the

molded plastic that is there to reinforcethe fixture f o r t h e industrial

environment, but with the color LEDs,they’re able to get kind of a cool decorative

effect because the light travels on the edges ofthe reinforcing element. What they’re doing withthe color is adding some interest to it.”

She also saw demonstrations of LED footpathsystems, for example, to mark a pathway orilluminate a perforated steel element such as anelectrical-cord cover. LEDs also showed up inhandheld inspection devices.

As to applications beyond the niches, they stillawait the crossing of the 100 lm/W bar. “The earliestI could see LEDs enter the mainstream ofmanufacturing environment would be probably bearound 2012, when we would have at least 100 lm/W and preferably maybe 150 lm/W. Then thingschange dramatically,” says David Pelka, presidentof Tailored Optics Inc. (Los Angeles, CA).

For now, the industry just keeps moving.“There’s been a lot of progress,” says Steele. “Thebest white LEDs are now three times as efficientas incandescent and getting pretty close tocompact fluorescents. After that, they’ll be hittingthe efficiency of linear fluorescents, and I thinkthat’s going to have an impact.”

—Kristin Lewotsky is a freelance technology writerbased in Amherst, NH.

Learn more about the latest breakthroughs inLEDs at the Illumination Engineering conferenceat Optics & Photonics this August in San Diego,CA. Find out more at spie.org/events/op.