Sulfur lamp

The sulfur lamp (also sulphur lamp) is a highly efficient full-spectrum electrodeless lighting system whose light is generated by sulfur plasma that has been excited by microwave radiation. They are a particular type of plasma lamp, and one of the most modern. The technology was developed in the early 1990s, but, although it appeared initially to be very promising, sulfur lighting was a commercial failure by the late 1990s. Since 2005, lamps are again being manufactured for commercial use. The sulfur lamp consists of a golf ball-sized (30 mm) fused-quartz bulb containing several milligrams of sulfur powder and argon gas at the end of a thin glass spindle. The bulb is enclosed in a microwave-resonant wire-mesh cage. A magnetron, much like the ones in home microwave ovens, bombards the bulb, via a waveguide, with 2.45 GHz microwaves. The microwave energy excites the gas to five atmospheres pressure, which in turn heats the sulfur to an extreme degree forming a brightly glowing plasma capable of illuminating a large area. Because the bulb heats considerably, it may be necessary to provide forced air cooling to prevent it from melting. The bulb is usually placed at the focus of a parabolic reflector to direct all the light in one direction. It would be impossible to excite the sulfur using traditional electrodes since the sulfur would quickly react with and destroy any metallic electrode. A patent pending to employ coated electrodes is discussed in Future prospects below. The absence of electrodes allows for a much greater variety of light-generating substances to be used than those used in traditional lamps. The design life of the bulb is approximately 60,000 hours. The design life of the magnetron has been improved by the Germany/England based Plasma International so it can also last for that same period. The warm-up time of the sulfur lamp is notably shorter than for other gas discharge lamps, with the exception of fluorescent lamps, even at low ambient temperatures.