Electrodeless Microwave-Driven Sulphur Lamp

The Sulphur lamp was invented by Michael Ury over the period 1986-1990, the principal reason for his interest being that the spectral distribution of its energy is very closely matched to the sensitivity of the human eye. Owing to the completely molecular radiation produced by sulphur, the spectrum is continuous and good colour rendering indices can be attained. Once the high efficacy of the discharge had also been demonstrated the patents were licensed to Fusion Corp. of Rockville, MD, U.S.A. who manufactured and marketed it.

The extreme electronegativity of sulphur means it is fiercely corrosive towards many materials found in other lamps. Tungsten electrodes are attacked and destroyed very rapidly, thus it is necessary to create an electrodeless lamp. Power is coupled to the discharge using a magnetron operating in the microwave frequency range, but efficiencies of 70% at best were attainable here. Because of the large bulb size convection currents are also a serious issue, and to deliver the temperature uniformity required to attain full vapour pressure of the sulphur (5 atm.), it is necessary to slowly rotate the bulb horizontally about the axis of the quartz support rod. The argon filling acts as a starting aid.

The spectral output peaks at 510nm, imparting a distinctly greenish hue to the illuminated environment and this is something which has proved to be a major obstacle in its marketing. It was also found to be impractical to make the system in lower wattages than with the 1000W lamp shown here. Sulphur lamps were trialled in many applications, most notably using 3M's light pipe system. But the green colour, restriction to high wattages, inefficiency of the magnetron and noise from its cooling fans saw the lamp axed in 2000.
Manufacturer: Technical University of Eindhoven / Philips
Lamp Power: 1,000 Watts
System Power: 1,375 Watts
System Frequency: 250 kHz
Cap: Quarz rod 4mm dia.
Bulb Finish: Clear
Bulb Type: 36mm dia. quartz sphere 32mm internal diameter
Overall Length: 150 mm
Light Centre Length: N/A
Electrodes: N/A
Atmosphere: Sulphur - 26mg (5 bar) Argon - 75 torr
Luminous Flux: 130,000 lm @ 100 hours
Luminous Efficacy: 130 lm/W @ 100 hours 95 lm/W system efficacy
Colour Temperature & CRI: CCT: 6000K CRI: Ra 79
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Horizontal with bulb rotation about axis of quartz rod
Rated Life: 60,000 Hours (Lamp) 20,000 Hours (magnetron)
Warm Up / Re-strike Time:
Factory: Eindhoven, The Netherlands
Date of Manufacture: 1999
Original / Present Value:
References: 1) Transport and Equilibrium in Molecular Plasmas: The Sulphur Lamp, Colin Johnston. Ph.D Thesis, Technische Universiteit Eindhoven, 2003.