Putting bright ideas to work

Although solid state lighting technology in making inroads in some markets, it faces challenges in industrial applications, reports Kristin Lewotsky in a recent article in SPIE Professional.

Lighting is poised to be the next great solid-state frontier. The technology is already making inroads in the markets for architectural lighting, signage, and specialty residential and retail applications.

According to Robert Steele, director of optoelectronics programs at Strategies Unlimited (Mountain View, CA), the overall lighting market for LEDs in 2005 was an estimated $250 million. Hard numbers arent yet available, but he projects the market to reach roughly $1 billion by 2010, with steady year-over-year growth rates of 30 to 40% annually. 'Its still small but its emerging,' he says. 'Theres a huge amount of activity.'

One of the strengths of LED lighting is reliability, making the industrial market a natural target of opportunity. In an industrial setting, replacing burned out bulbs doesnt just incur parts costs but also production downtime costs. Given the industrial settings voracious appetite for lumens, however, LED lighting is going to have to meet some pretty strict performance standards.

Industrial Strength

LEDs generate white light through a mix of red, green, and blue output or by downconversion via phosphors. In theory, the technology offers high efficiency; the reality is lagging a bit.

According to 'Solid-State Lighting Research and Development Portfolio,' a U.S. Department of Energy (DoE) roadmap compiled in conjunction with a panel of industry experts, current white-light LEDs can produce from 20 to 45 lm with a luminous efficiency of 20 lm/W or 45 lm/W, respectively. In contrast, a typical fluorescent bulb produces 5300 lm at a luminous efficiency of 83 lm/W, and a high-intensity discharge bulb produces 24 klm at a luminous efficiency of 80 lm/W. Clearly, LEDs are at an enormous disadvantage in terms of overall output, despite boasting lifetimes a factor of two or more higher than the other technologies.

Industry doesnt care as much about lifetime if it cant get the light it needs for an assembly line or a high bay, though. 'For these particular applications, I think the requirement is still tens of thousands of lumens,' says Srinath Aanegola, director for white LED technology at GELcore (Valley View, OH), and a member of the technical committee for the DoE report. 'Whether solid-state lighting will be the right choice is still a question mark.'

Power On

Of course, the aforementioned DoE roadmap carries two important milestones: reaching an efficiency of better than 100 lm/W by 2010 and reaching 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 efficiencies typically drop by 50% when devices are scaled up to the large chips and color temperatures appropriate for industrial applications.

Past the magic 100 lm/W barrier, a whole host of interesting things happen. LEDs will provide better luminous efficiency and lifetime than any lighting alternative, on a competitive cost basis.