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* Making Smart Lighting Possible

For some smart lighting applications, “design tunability” (fabrication of LEDs that have the desired color, polarization, etc.) will be adequate, Schubert says. Structural control can be provided by the use of photonic crystals, reflectors, and cavities (resonator structures with deliberate defects that control photons).

Real-time tunability will be required, however, for such applications as lighting, imaging, and communications. Schubert plans to achieve real-time tunability by designing devices that include multi-channel electrical and optical controls. Because such factors as temperature and voltage can affect the properties of the light emitted, it is possible to tune the light by controlling these factors. The controls could also be used to activate various portions of a photonic crystal.

With incandescent lights independent tunability of color and intensity is not possible, Lin says, because increasing intensity raises the heat and shifts the color spectrum. With LEDs, the color is largely determined by the material, which is deposited in layers. Color shifts must be obtained by using several different colors of LEDs in an array. Photonic crystals, however, are created by lithography, the technology used to fabricate computer chips. One chip could be designed to carry several colors or intensities, making very precise tunability possible.

Much basic science and computer modeling is still needed, however, to understand what light characteristics are best for specific applications and how to design tunable LED arrays and photonic crystals which produce the desired light. A number of research projects are under way to develop the needed technology, particularly work in materials, photonic crystals, and improvements to LED devices. See:

One problem, for example, is that current systems do not extract all of the light from an LED, both because of poor reflectivity and because polymers used to encapsulate the working structure lose transparency in reaction to the light, particularly in short-wavelength and high-power emitters.

Schubert is developing an omni-directional reflector that makes it possible to extract more than 99 percent of the light from both inorganic and organic LEDs. This reflector consists of a semiconductor layer, a dielectric (insulating) layer perforated by an array of micro-contacts, and a metal layer.

In the meantime, Rensselaer chemists and chemical engineers have synthesized new siloxane resins with superior qualities for LED encapsulation and low-refractive-index materials with unprecedented properties. The materials display excellent transparency and long-term stability. Further research is needed to improve mechanical and thermal properties.

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Related Web sites:

Rensselaer Research

Future Chips Constellation

Lighting Research Center

Center for Advanced Interconnect Systems Technologies

Interconnect Focus Center-New York

Center for Broadband Data Transfer Science and Technology

Nanotechnology Science and Engineering Research Center

Additional Information:

Rensselaer Receives NYSTAR Faculty Development Award

Rensselaer Completes Future Chips Constellation With Two New Faculty Appointments

Semiconductor Expert to Head Future Chips Research at Rensselaer

Blue LEDs for Those with Alzheimer’s

Big Chips in Little Packages

Broadband Center Off to Quick Start

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Turning the Dream Into Reality

The photonics revolution now under way already has provided tremendous benefits in energy savings, improved lighting, versatile new display technologies, and optical communications. Yet, the science and technology are still not available for the full control of many basic characteristics of light. As technical problems are overcome and new photonic products reach the marketplace, smart lighting will revolutionize such fields as illumination, imaging, display, and communications. Improved LEDs and new photonic crystal light emitters, moreover, are expected to greatly reduce the world’s consumption of energy and diminish harmful environmental impacts.

Formidable technical roadblocks remain, but the researchers in Rensselaer’s Future Chips Constellation are optimistic. They have come together at Rensselaer because they believe that working together in a multidisciplinary constellation focused on a common goal offers them the best opportunity to move the concept of smart lighting from dream to reality.

See also: Looking Into Light

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