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Innovations in smart lighting will spring from new photonic crystal light emitters that will be 10 to 30 times more efficient than light bulbs, says Shawn-Yu Lin, Future Chips Constellation Professor and professor of physics. They will have a huge impact on worldwide energy consumption and the environment. It will be possible to change their color and their intensity independently, so that a homeowner can easily adjust both to match the time of day, the current use of the area, or the mood of the occupants.

The Future Chips researchers are working on developing the light source for these technologies. “The computers are already very smart. They are waiting on us to provide the data,” says Christian Wetzel, the Wellfleet Career Development Constellation Professor, Future Chips, and associate professor of physics.

Schubert, Lin, and Wetzel — all recognized photonics pioneers — form the nucleus constellation, which also includes Thomas Gessmann, a research assistant professor of electrical, computer, and systems engineering; Jong Kyu Kim and Theeradetch Detchprohm, two postdoctoral researchers; and a number of doctoral students and three undergraduate students.

In addition, other Rensselaer research centers, including the Center for Advanced Interconnect Systems Technologies, the Interconnect Focus Center-New York, the Rensselaer/IBM Center for Broadband Data Transfer Science and Technology, the NSF Nanotechnology Science and Engineering Research Center, and the Lighting Research Center, provide a broad range of expertise, potential collaborations, and facilities for work in this emerging field.

A major focus of the constellation, smart lighting is a revolutionary new field in photonics based on efficient light sources that are fully tunable in terms of such factors as spectral content, emission pattern, polarization, color temperature, and intensity.

“The research program in the Future Chips Constellation aims at nothing less than transforming many sectors of the economy, including communications, medicine, defense, entertainment, and the environment,” Rensselaer President Shirley Ann Jackson says. “We are delighted to have these stellar individuals join our dynamic research environment, working to develop next-generation technology in semiconductor design and performance.”

Schubert says smart lighting will not only offer better, more efficient illumination, it will provide “totally new functionalities.” For example:

Studies have shown that spectral (color) variations in light have profound effects on the human circadian and visual systems. Controlling the amount of red, yellow, and blue in white light has implications for sleep in Alzheimer’s patients, growth of premature infants, seasonal depression, jet lag, and the well-being of night-shift workers. Some researchers have suggested that inappropriate lighting can upset the body chemistry and even lead to certain types of cancer.

In live-cell biological imaging, smart lighting could make it possible to coordinate intensity, wavelength, and polarization with image scanning to reveal a new wealth of features. Using this revolutionary cellular microscopy technique, for example, researchers could observe and analyze multiple single cells in real time as they react to a drug or infectious agent.

Shawn Yu-Lin
Central and peripheral vision react to different color spectrums. Automobile headlamps with dispersive characteristics perfectly adapted to human vision characteristics could provide enhanced visibility and safety for nighttime driving.

Smart lighting could address the world’s pressing need for increased food production because light plays a pivotal role in plant growth and photosynthesis. Adjustable smart-light sources predominately made up of blue, red, and infrared wavelengths — the portions of the spectrum best absorbed by plants — could provide a low-cost, energy-efficient way to grow crops off-season.

The “Century of the Photon”
Such technologies are possible, Schubert says, because of advances in photonics that are transforming society just as electronics revolutionized the world in recent decades. In fact, some have called this the “century of the photon.” North America’s optoelectronics market grew to more than $20 billion in 2003. The LED (light-emitting diode) market is expected to reach $5 billion in 2007, and the solid-state lighting market is predicted to be $50 billion in 15 to 20 years, Schubert says.

LEDs are specialized semiconductor devices that can potentially convert electricity to light, without the wasteful creation of heat. The color emitted is controlled in large part by the energy gap of the semiconductor and in advanced structures by the “photonic band gap,” a range of wavelengths that cannot travel through that particular substance. By suppressing certain wavelengths and enhancing others, the band gap determines the color.

LEDs commonly are used for indicator lights, displays on consumer electronics, exit signs, traffic signals, and roadwork signs. The first LEDs, which were made of GaAsP (gallium arsenide phosphide), emitted red light. New materials and technologies made amber, green, and blue LEDs possible. Now that several types of white LEDs have become available, manufacturers are looking beyond the specialized display market to the use of LEDs for general illumination, television monitors, and large-area displays.

Researchers also are exploring new organic materials (polymers) for the fabrication of organic light-emitting diodes. The goal is to use these light-emitting polymers to create thin, flexible sheets of light. Light-emitting wallpaper or even clothing may be possible.

Christian Wetzel
A World-Class Team
Schubert arrived at Rensselaer from Boston University in late 2002 to head the new constellation. He holds 28 issued patents and invented the resonant cavity LED that helped transform traffic signals and airport runway lighting, as well as the photon-recycling semiconductor LED, a promising new approach to the challenge of white LEDs.

Wetzel, who joined the team last spring, is known for his work in materials physics and the chemistry of light emission. Since the early 1990s, he has explored the use of gallium nitride compounds for LEDs, first at Berkeley and next in Japan in the lab of Isamu Akasaki, where gallium nitride materials were used to pioneer the fabrication of blue LEDs. With Uniroyal Optoelectronics in Tampa, Fla., Wetzel developed successful MOCVD (metal organic chemistry vapor deposition) techniques to produce very intense green LEDs.

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