Evolution drives revolution in solid-state lighting

Driven by continuous technological development, high-brightness light-emitting diodes (LEDs), along with nontelecommunications laser diodes, provided one of the bright spots in the optoelectronics market in 2002.

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Driven by continuous technological development, high-brightness light-emitting diodes (LEDs), along with nontelecommunications laser diodes, provided one of the bright spots in the optoelectronics market in 2002. Both of these sectors grew by about 50% last year. At the same time, semiconductors remained level and the telecommunications optical-component market continued to fall to about two-thirds its 2001 levels, according to Robert Steele, director of optoelectronics at Strategies Unlimited (Mountain View, CA). Steele spoke at the annual Strategies in Light conference last month, at which the bounce-back from 2001 was in evidence by the conference room packed with 240 attendees and a strongly upbeat mood.

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FIGURE 1. The quotation on the interior dome frieze of the Jefferson Memorial ("I have sworn upon the altar of God eternal hostility against every form of tyranny over the mind of man") is illuminated by 17,000 light-emitting diodes spanning 750 linear feet.
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Demand for indium gallium nitride chips also grew by more than 70% in 2002, with Taiwanese companies emerging as major suppliers to provide blue illumination primarily for mobile-phone keypads, Steele noted. Overall, the number of suppliers of white-emitting LEDs has more than doubled during the last two years. In addition, numerous intellectual-property (IP) lawsuits have been settled and cross-licensing agreements inked—several with Nichia—as the various competitors in the industry continue to move forward on their common technology and market.

The intellectual property required to fully develop high-brightness solid-state lighting sources is not all contained in one country or even one company, and pooling of IP will be required for solid-state technology to ultimately move toward the long-sought goal of general illumination, according to Schiu Sche, a senior advisor at Opto Tech (Hsin Chu, Taiwan) and chairman of the optoelectronics committee of the Taiwan Electric & Electronic Manufacturer's Association (Taipei, Taiwan).

Storm clouds, on an otherwise bright horizon, that can't be controlled include the possibility of war that threatens to significantly reduce capital, consumer, and government spending on peacetime civilian applications. These applications include large video signs, automobiles, mobile phones, and traffic signals, all of which fueled the emergence of the high-brightness LED market and brought about last year's recovery, Steele said.

Evolving technology

The overwhelming focus on national security issues is also a barrier to the passage of energy legislation to fund the proposed Next Generation Lighting Initiative (NGLI), according to Pamela Farrell, a business development manager at GE Global Research (Niskayuna, NY). "I think that we have enough support in Congress and that NGLI will make it to the table in 2003," said Farrell, a lobbyist for the NGLI. The House and Senate approved a proposal last year, but a final version was not passed before Congress adjourned. "Energy bills are hard," Farrell said. "NGLI gets swamped in arguments about other issues, like oil drilling."

Key technology and marketing issues discussed by various speakers included packaging, measurement, design innovation, and cost. Packaging strategies, such as improving upon or replacing epoxy encapsulants or lenses, as well as various innovative heat-sinking methods, are playing a key role in providing both the light-extraction efficiencies and thermal management required for LED light sources to actually provide longer service lifetimes than traditional sources.

Speakers from the National Institute of Standards and Technology (NIST; Gaithersburg, MD), Rensselaer Polytechnic Institute (RPI; Troy, NY) and several presenting companies addressed the inadequacy of color-rendering index as a metric, not only for evaluating LEDs, but also for providing an accurate assessment of viewer preference under various lighting schemes. According to conventional wisdom, the color-rendering index indicates the color-rendering properties of a light source, according to Nadarajah Narendran, director of research at the RPI Lighting Research Center. But in actuality, CRI only evaluates how object colors conform to illumination by a standard source, which in most cases is incandescent. Because incandescent illumination is deficient in blue, if an illumination source provides a better balance than incandescent (more blue) the CRI will actually go down.

Functional as opposed to device-design factors include whether to design solid-state light "bulbs" that can plug or screw into the tremendously large installed base of traditional light sockets or to "reinvent lighting," which involves asking different questions, according to Makarand Chipalkatti, director of lamp modules in North America for Osram Opto Semiconductors (Regensburg, Germany). Rather than designing LEDs to replace certain bulb types, for example, the question might be how to illuminate a space or surface to get a desired illuminance (see Fig. 1 and Fig. 2).

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FIGURE 2. Rather than simply replacing conventional bulbs, solid-state lighting is enabling new design strategies such as using chips in the railing to provide walkway lighting.
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John Nylander of OptiLED (Irvine, CA) emphasized the need for conducting the LED lighting revolution in the market through an evolutionary process of technology development. "The penetration of LEDs into the lighting market depends on the development of integrated, easy-to-use LED-based lamps," he said. Market acceptance of new LED lamp fixtures rather than replacement LED "bulbs" for existing fixtures requires a strongly market-oriented cost model, Nylander added. "We started with what we thought the market would accept and cut it in half," he said. "And in terms of commercial applications, you must get return on investment within one year, within the budget cycle. We've hit a nine-month payback cycle."

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