Updated 25-VIII-2003
Mercury Vapour
Mercury Pressure
Mercury Spectrum
Lamp Nomenclature
Timeline of Developments
Mercury Vapour
J.T. Way
Küch and Retschinsky
MA Medium Pressure
MB High Pressure
MC Low Pressure
MD Water-Cooled
ME Super Pressure
UHP Ultra High Pressure
Mercury Vapour
Fluorescent Coated Lamps
Tungsten Ballasted Lamps
Lamp Electrodes
Additives to the Arc
Electrodeless Designs
Future Developments
Mercury Vapour
High Pressure Circuits
Low Pressure Circuits
Electronic Operation

Küch & Retschinsky's Lamp

The next milestone in mercury lamp development was laid in the summer of 1906, when there appeared in the Annalen der Physik a paper by Küch and Retschinsky concerning the production of light by a high pressure mercury discharge.

Their lamp resembled a scaled-down model of the Cooper-Hewitt, but it was fabricated from quartz glass and employed two electrodes of liquid mercury.  Ignition was performed by tilting the lamp so that a thread of mercury short-circuited the electrodes, the arc being started by levelling the tube and breaking the contact between the electrodes.  The lamps were still DC operated.  Quartz, being a much more refractory material than the hard glasses employed by Cooper-Hewitt, could endure much higher electrical loadings under which conditions the lamp efficacy rises.  Such conditions naturally led to higher temperatures and higher mercury pressures as well.  The inventors managed to attain pressures of several atmospheres, at which a luminous efficacy of about 50 lumens per watt was achieved.  Figure 16 shows a photograph of their lamp.

Figure 16 - The high pressure quartz lamp of Küch and Retschinsky

Although these quartz lamps were manufactured by Westinghouse (via the Cooper-Hewitt company) and later by GE, they were not practical as light sources for general lighting.  The quartz envelope allowed allowed the lamp to transmit dangerously high levels of ultraviolet radiation, which incidentally developed another niche for their application - as artificial UV lamps for sun-tanning and other therapeutic uses.

Additionally , and there existed no reliable method for sealing metal conductors into quartz.  These early lamps employed seals in which precisely shaped conical indentations were ground into the quartz ends of the lamp, and each had to be individually tailored to mate with a tapered invar pin of identical dimensions, the whole being immersed in mercury.  If the lamps didn't leak when new, they lasted only a relatively short time in service before failure of the seals brought the lamps to the end of their life.

Figure 17 - Quartz-Invar Seal

It was also required, for safety reasons, to prevent the mercury pressure rising too high under which conditions the lamp could explode.  Commercially available lamps were therefore equipped with metal fins clamped to the arc tube around the mercury electrodes, serving to reduce the temperature here and keep the pressure within safe limits.  They were most commonly employed in scientific or medical applications, for instance as ultra-violet sun lamps used in the treatment of various skin conditions.