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Lighting — The Next Generation
The following article prepared by Stephen Turner and Robert Farmer is based on a TRENDS report by Seth Shulman in the January 1996 issue of Technology Review, © Massachusetts Institute of Technology.
A lighting technology with better color temperature and color rendering index than incandescent, better lamp life than fluorescent, at an efficiency of 100 lumens per watt?
Yes, sulfur lighting—and it is on the verge of becoming a viable commercial technology. If you want to see this exciting technology from newcomer Fusion Lighting, you’ll have to go to the Air and Space Museum, or the Department of Energy headquarters in Washington, DC. But don’t go looking for a conventional lamp. Each sulfur bulb generates so much light it takes only six small bulbs, one at each end of three “light pipes” spanning the ceiling of the museum, to provide all of the illumination.
The light from the sulfur bulbs is focused into each end of the acrylic “pipe” by parabolic reflector where it is bounced back and forth off reflecting film until it finds its way downward through a special light-transmissive film running along the underside of the pipe, illuminating the building below.
The Department of Energy used one sulfur fixture to replace 240 175-watt mercury fixtures. The Department reports a quadrupling in light levels and energy savings of 60%. The quality of light earned the technology a place in the exhibit hall of the Air and Space Museum, where three light pipes replaced 94 High Intensity Discharge mercury fixtures.
Most light sources are atomic emitters—photons pop out when excited electrons drop back to lower energy states. (Remember that 2p, 4p stuff from chemistry?) This limited process results in a “signature distribution” of photons—light with specific characteristics. The tungsten in incandescents gives off a warm, yellowish light. The mercury in fluorescents typically results in a cooler, greenish glow.
Then, in 1990, sulfur was discovered to be a molecular emitter. A pinch of sulfur is sealed with argon gas in a small quartz bulb. When the mixture is exposed to electromagnetic waves at 2.4 billion cycles per second (the range of a microwave oven) it vaporizes into diatomic sulfur molecules. In this special, excited state the mixture yields a large, unusually rich mixture of photons—almost all in the visible spectrum. The result is intense, white light. And the broad spectrum light emitted emulates sunlight better than any artificial light source yet discovered.
Fusion Lighting in Rockville, Maryland is developing a 5,900 watt sulfur bulb called Solar 1000. Pricing is expected to be competitive with existing technologies, but has not yet been announced. Every major lighting company in the world, including GE, Philips, Osram and Matsushita, has shown interest in the technology.
These companies no doubt recall the speed at which fluorescent lights captured much of the lighting market after being introduced at the Chicago Centennial Exposition in 1933. Fluorescents came into popular use by 1939, and within ten years dominated the institutional marketplace.
But for the time being the future for sulfur lights seems limited to higher lumen applications. The magnetrons needed to generate the microwaves and the motors needed to rotate the mixture in the bulbs and keep them cool with ambient air are only available in the 250 watt range at present. To make a workable 150 watt bulb, the sulfur bulb would need the equivalent of a 15 watt magnetron.
Look for the larger lights in outdoor and large scale applications within a couple of years, and keep tabs on this exciting technology—it may soon become part of your retrofit plans! •
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