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foil lamps outshine incandescent lights
E. Kloeppel, Physical Sciences Editor
photo to enlarge
by L. Brian Stauffer
Eden, professor and director of the Laboratory
for Optical Physics and Engineering, left, with
Sung-Jin Park, visiting professor and research
scientist in electrical and computer
engineering, hold flat-panel lamps made with
aluminum foil and tiny plasma arrays their team
CHAMPAIGN, Ill. — Researchers
at the University of Illinois are developing panels of microcavity plasma
lamps that may soon brighten people’s lives. The thin, lightweight
panels could be used for residential and commercial lighting, and for
certain types of biomedical applications.
photo to enlarge
of an aluminum foil lamp having a radiating area of
225 square centimeters. The inset is a magnified view
of several diamond-shapes microcavities.
aluminum foil, sapphire and small amounts of gas, the panels are less
than 1 millimeter thick, and can hang on a wall like picture frames,”
said Gary Eden, a professor of electrical
and computer engineering at the U. of I., and corresponding author
of a paper describing the microcavity plasma lamps in the June issue
of the Journal of Physics D: Applied Physics.
Like conventional fluorescent lights, microcavity plasma lamps are glow-discharges
in which atoms of a gas are excited by electrons and radiate light.
Unlike fluorescent lights, however, microcavity plasma lamps produce
the plasma in microscopic pockets and require no ballast, reflector
or heavy metal housing. The panels are lighter, brighter and more efficient
than incandescent lights and are expected, with further engineering,
to approach or surpass the efficiency of fluorescent lighting.
The plasma panels are also six times thinner than panels composed of
light-emitting diodes, said Eden, who also is a researcher at the university’s
Coordinated Science Laboratory and the Micro and Nanotechnology Laboratory.
A plasma panel consists of a sandwich of two sheets of aluminum foil
separated by a thin dielectric layer of clear aluminum oxide (sapphire).
At the heart of each lamp is a small cavity, which penetrates the upper
sheet of aluminum foil and the sapphire.
is approximately the diameter of a human hair,” said visiting
research scientist Sung-Jin Park, lead author of the paper. “We
can pack an array of more than 250,000 lamps into a single panel.”
Completing the panel assembly is a glass window 500 microns (0.5 millimeters)
thick. The window’s inner surface is coated with a phosphor film
10 microns thick, bringing the overall thickness of the lamp structure
to 800 microns.
photo to enlarge
diagram of a flat lamp structure based on aluminum
foil encapsulated in saphire and a thin glass coating.
The lower right portion of the figure presents photographs
at two magnifications of an electrode screen with
diamond cross-sectional microcavities. The smallest
graduation of the scale is 1 millimeter.
Flat panels with
radiating areas of more than 200 square centimeters have been fabricated,
Park said. Depending upon the type of gas and phosphor used, uniform
emissions of any color can be produced.
In the researchers’ preliminary plasma lamp experiments, values
of the efficiency – known as luminous efficacy – of 15 lumens
per watt were recorded. Values exceeding 30 lumens per watt are expected
when the array design and microcavity phosphor geometry are optimized,
Eden said. A typical incandescent light has an efficacy of 10 to 17
lumens per watt.
The researchers also demonstrated flexible plasma arrays sealed in polymeric
packaging. These devices offer new opportunities in lighting, in which
lightweight arrays can be mounted onto curved surfaces – on the
insides of windshields, for example.
The flexible arrays also could be used as photo-therapeutic bandages
to treat certain diseases – such as psoriasis – that can
be driven into remission by narrow-spectrum ultraviolet light, Eden
With Eden and Park, co-authors of the paper are graduate students Andrew
Price and Jason Readle, and undergraduate student Jekwon Yoon.
Funding was provided by the U.S. Air Force Office of Scientific Research
and the Office of Naval Research.
Editor’s note: To reach Gary Eden, call
217-333-4157; e-mail: email@example.com.