New Lighting Approach Is a Gas
WASHINGTON, Nov. 28, 2011 — Just as in a fluorescent light, a microcavity array (MCA) is energized by an applied voltage. By successfully confining plasma (an ionized gas) in parallel rows of microcavities within thin sheet materials, various implementations of microplasma arrays have been achieved, resulting in inexpensive, wafer-thin, flexible sheets of light.
The discovery was made by Drs. Gary Eden and Sung-Jin Park of the University of Illinois at Urbana-Champaign, who co-founded Eden Park Illumination Inc. to bring the new technology to market. The lighting technology company was founded in 2007 and is a close affiliate of the Laboratory of Optical Physics and Engineering at the university. The research was funded by the Air Force Office of Scientific Research.
The discovery began to take shape in 1996, when two graduate students approached Eden with a block of silicon and asked whether they could drill a small hole in it to try to produce a plasma inside the hole. Eden said they did, in fact, produce a plasma inside a hole with a diameter of about 400 µm, which he said was a crude forerunner of the current MCA lighting system.
A research team funded by the Air Force Office of Scientific Research has pioneered the use of microplasmas in a revolutionary approach to illumination. Just as in a fluorescent light, a microcavity array is energized by an applied voltage. By successfully confining that plasma in parallel rows of microcavities within thin sheet materials, Drs. Gary Eden and Sung-Jin Park of the University of Illinois at Urbana-Champaign ultimately arrived at various implementations of microplasma arrays that result in inexpensive, wafer-thin and very flexible sheets of light. (Image: Eden Park Illumination)
Eden said he was intrigued by the issue of space and pressure. A fundamental rule for stable, steady-state plasma is pressure times diameter scaling — the smaller the plasma dimensions, the higher the pressure can be. The very high pressures that can thus be obtained in microplasmas give rise to unique lighting and other properties.
The microcavities formed within the flexible sheets are key to these light arrays. In one of the most important implementations, the one being developed by Eden Park Illumination, a sheet of aluminum foil is placed in an anodizing bath. By controlling the bath parameters — its temperature and the time of anodizing — large arrays of microcavities can be formed with near-optimum shape and with automatically placed interconnecting aluminum electrodes. The largest array thus far contains one-quarter million luminous microcavities. Thin laminated films on the surface of the wafer contain the electrical power interconnects that feed the individual cavities. When A/C power is supplied through the almost-invisible grid, the array bursts to life.
The largest arrays currently being produced are 6 inches square. These can be conveniently tiled together, in different colors if desired, to make larger arrays; if desired, much larger arrays can be made, limited only by the size of the anodizing bath. Conveniently, aluminum foil is used, with a thickness of 125 µm. The cavities are then sealed in very thin sheets of glass, resulting in an array that is 1 to 2 mm thick.
The plasma arrays are ruggedized to a certain extent and have an ultimate thickness of about 4 mm, resulting in a wafer that weighs less than 200 g.
Compared to contemporary lighting, the MCA lighting has much greater efficiency due to its design. Because the array is flat, it does not lose the lumens per watt that a standard light does. The MCA lighting currently lasts 20,000 hours before failure.
A further advantage is that the MCA lighting is more environmentally friendly because it does not contain mercury, and its plastic, glass and aluminum contents are easy repurposed and recyclable.
Compared to that of LEDs, the MCA’s efficiency doesn’t quite measure up, but it does generate far less heat than LEDs, which means it runs cooler and doesn’t require an aluminum heat sink.
Because of the current rate of production, the MCA is not cost-competitive with current lighting options, but since Congress mandated that incandescent lights be phased out in 2014, the research team believes there will be a much greater acceptance of MCA technology and its applications.
Because microplasma arrays are lightweight, small, flat and flexible, and give off little heat, they have applications in a broad range of general and specialized lighting. The researchers said the technology is not only well-suited for light production but is ideal for on-chip special chemistries. And by utilizing the linear microchannel design, as employed in an MCA lighting panel, a large number of parallel receptors can be placed within a small area to perform a variety of sensory activities, depending on the chemical composition within the cavities.
For more information, visit: www.afosr.af.mil
- A gas made up of electrons and ions.
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