The sulfur 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, one of the most modern. The technology was developed in the early 1990s, but although it initially seemed very promising, sulfur lighting was a commercial failure in the late 1990s. Since 2005, lamps for commercial use have been manufactured again.

Sulfur plasma is mainly composed of dimer molecules "Dimer (chemistry)") (S2), which generate light through molecular emission. Unlike atomic emission, the emission spectrum is continuous throughout the visible spectrum. Up to 73% of the radiation emitted is in the visible spectrum, with a small amount in infrared energy and less than 1% in ultraviolet light.

The emission spectrum reaches a maximum of 510 nanometers, giving the light a greenish hue. The correlated color temperature is approximately 6,000 kelvins with a color rendering index of 79. The lamp can be dimmed to 15% without affecting light quality.

A magenta filter can be used to give the light a warmer feel. This filter was used in the lamps at the United States National Air and Space Museum in Washington D.C.[1]​.

Adding other chemicals to the bulb can improve color rendering. Sulfur lamp bulbs with calcium bromide (CaBr2) produce a similar spectrum plus a peak at red wavelengths at 625 nm.[2] Other additives such as lithium iodide (LiI) and sodium iodide (NaI) can also be used to modify the output spectra.[3]

The technology was conceived by engineer Michael Ury, physicist Charles Wood and their colleagues in 1990. With support from the United States Department of Energy, it was developed in 1994 by Fusion Lighting in Rockville, Maryland, a division of Fusion Systems Corporation. Its origins are in microwave discharge light sources used in the semiconductor and printing industries. The division was later sold to Spectris plc, and the remainder of Fusion Systems was subsequently acquired by Eaton Corporation.

Only two production models were developed, both with similar specifications: the Solar 1000 in 1994 and the Light Drive 1000 in 1997, which was an improvement on the previous model.