Thin Foil Lamps Outshine Bulbs

Lamps the diameter of a human hair, made with foil and tiny plasma arrays, are being developed for use in residential and commercial lighting and some biomedical applications.

“Built of 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 University of Illinois, and corresponding author of a paper describing the microcavity plasma lamps.

Gary Eden, professor and director of the University of Illinois 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 developed. (Photo by L. Brian Stauffer)

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 LEDs, 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.

Photograph of an aluminum foil lamp having a radiating area of 225 sq. cm. The inset is a magnified view of several diamond-shaped microcavities.

“Each lamp is approximately the diameter of a human hair,” said visiting research scientist Sung-Jin Park, lead author of the paper, which appears in the June issue of Journal of Physics D: Applied Physics. “We can pack an array of more than 250,000 lamps into a single panel.”

Completing the panel assembly is a glass window 500-µm (0.5 mm) thick. The window’s inner surface is coated with a phosphor film 10 µm thick, bringing the overall thickness of the lamp structure to 800 µm. 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 lpW 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 lpW.

Cross-sectional 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 mm.

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 phototherapeutic bandages to treat certain diseases -- such as psoriasis -- that can be driven into remission by narrow-spectrum ultraviolet light, Eden said.

Other co-authors of the paper are graduate students Andrew Price and Jason Readle, and undergraduate student Jekwon Yoon. Funding was provided by the US Air Force Office of Scientific Research and the Office of Naval Research.

For more information, visit: www.uiuc.edu