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New light source
I found this article in the February 1995 Popular Science:
Lighting: Bright Light, Small Bulb
by Mariette DiChristina
Photo caption:
"In this new light bulb, sulfur excited by microwaves emits a bright
white light. At the DOE's headquarters, a sulfur bulb at each end of
one 240-foot-long light pipe replaced 240 individual 175-watt
high-intensity lamps. One Tootsie-Pop-size lamp gives off the same
light as more than 250 standard 100 watt incandescent bulbs."
It has roughly the dimensions of a Tootsie-Pop, but don't let the
diminutive size fool you: Sparked by microwaves, a new sulfur bulb
packs a lighting wallop. One 5,900 watt bulb generates the same amount
of light as hundreds af today's industrial high-intensity
mercury-vapor lamps - using 20 to 30 percent less energy.
"It's a major breakthrough in lighting," says Christine Ervin of the
Department of Energy. Unlike conventional lighting, sulfur bulbs have
no electrode to wear out. That means the bulbs could operate as long
as the microwave generators (10,000 to 15,000 hours). While this is
comparable with today's high intensity lamps, those typically dim to
half their original output by that time because their phosphors
degrade. "We don't know how long it will lost ultimately," says Kent
Kipling of Fusion Lighting of Rockville, Md., which developed the bulb
under a DOE contract.
The sulfur bulbs were combined with plastic "light pipes" from 3M for
testing at two installations in Washington, D.C. - DOE's headquarters
at the Forrestol Building and the Smithsonian's Air & Space Museum.
DOE says the two test installations cost less than half the price of
the conventional lighting systems they replaced.
The sulfur bulb's hollow quartz sphere contains a small amount of
inert argon gas and yellow sulfur powder. To generate light, the bulb
is spun at 600 rpm and is simultaneously bombarded with microwaves in
a compact generator cavity originally developed for ultraviolet
industrial technology. Heated by the argon. the sulfur powder boils
Into a vapor and emits a bright white light. This light is projected
by a reflector into long plastic pipes lined with a semi-reflective
film with either a mirror or a second bulb at the far end. The light
zig-zags along the pipe, with some of it directed through the film for
illumination of an area.
The sulfur technology may sound simple to develop. But like many movie
stars, the bulb is a ten-year "overnight" success. For example, it
requires a special microwave cavity, which had been refined over
decades for industrial uses. "We must have spent more than 100
man-years to get to this point," says Michael Ury, one af the bulb's
inventors.
Sulfur had also never been tried in lighting before, says Ury, because
it oxidizes metals - and so would degrade the electrodes used in
conventional bulbs. "We were always trying new ideas, crazy ideas," he
says. "I guess we just wanted to be different." Serendipitously,
Ury's colleague James Dolan picked the right microwave cavity and the
right rpm to spin the bulb on the first try. "If we didn't get
everything together like that, we might have missed it," ssys Ury.
In addition to its energy efficiency and long life, the sulfur bulb
offers other benefits. Because its bright white light is similar to
natural light, it is more aesthetically pleasing than the blue-white
color of high-intensity mercury-vepor lamps or some fluorescent lamps.
Plants may prefer it as well: NASA has a two-year contract with Fusion
to develop its light for growing plants in space. And the new bulb
produces far less of the fabric-fading ultraviolet rays generated by
other industrial lamps - a bonus for fragile museum exhibits as well
as home furniture. The disposal af mercury containing lamps also has
been an environmental problem.
While sulfur bulbs will first illuminate large spaces like shopping
centers, aircroft hangers, and factories, home applicafions are also
under development. Commercial products could appear within two yeors.