Updated 24-VII-2023
Mercury Vapour
Mercury Pressure
Mercury Spectrum
Lamp Nomenclature
Timeline of Developments
Mercury Vapour
J.T. Way
Lamp Design
Manual Starting
Automatic Starting
Exhausting Process
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

The Cooper-Hewitt Lamp

Around the turn of the century, the first mercury lamp to become a commercial success was created by the American inventor Peter Cooper-Hewitt, Figure 8.  By 1901 his development was complete and a year later he founded the Cooper-Hewitt Electric Co. of New York, backed with money from George Westinghouse.

His low-pressure mercury discharge radiated copious amounts of blue and green light but was severely deficient in red, and had the most appalling colour rendering ability.  Despite its guaranteed ability to transform even the most beautiful human subject into a ghastly cadaverous specimen, it enjoyed remarkable success in industrial lighting.  Lighting economics was the reason, and it had not gone unnoticed that for the same electricity consumption, mercury lamps put out many times more light than the carbon filaments.

Figure 8 - Peter Cooper-Hewitt
Figure 9 - A Blended Lamp
In 1902 the inventor stated "When it is considered that this light, when obtained with mercury gas, has an efficiency at least eight times as great as that obtained by an ordinary incandescent lamp, it will be appreciated that it has its use in places where lack of red is not important, for the economy of operation will much more than compensate for the somewhat unnatural colour given to illuminated objects"

Improving the colour was tackled through an early use of fluorescent materials, whereby reflectors around the lamp were given a coat of the rosy coloured dye Rhodamine.  An alternative invention of Cooper-Hewitt was to employ series-wired carbon filament lamps to act as the ballast for his lamp, and these delivered a strong red contribution but did reduce efficacy somewhat. The example illustrated in Fig. 9 is the earliest ancestor of modern mercury blended lamps.

The light was also prone to flickering as the root of the discharge danced around on its electrode of boiling mercury, and although the inventor fine-tuned his lamp geometry to minimise this, the problem could not be eradicated.

Nevertheless the lamp enjoyed great success in industrial lighting the photo-printing business, which both required large amounts of cheap light and where colour was of little concern.  Fig. 10 shows a typical 1908 advertisement aimed at the printing industry.

Factory lighting is a market in which it gradually lost popularity though, as a result of the tremendous advances occurring in incandescent technology.  Within a decade or two the tungsten lamp had been developed to the state that it began to pose a serious threat to the sole stronghold of mercury - its previously unparalleled efficacy.
Figure 10 - A Typical 1908 Advertisement

The Cooper-Hewitt company embarked on a bold marketing campaign, often with rather extravagant claims that the lack of red radiation was in fact to be regarded as quite an advantage.  It was stated that the fatigue of the eyes produced by close work under artificial light was due almost entirely to the presence of 'harmful red rays' in the spectrum of the incandescent lamp.  The mercury lamp was subsequently promoted with renewed force in such applications as offices of draughtsmen, or in environments where close attention to books and papers is required

Eventually the more efficient tungsten filaments poached its place in industrial illumination, and the Cooper-Hewitt lamp was thereafter exiled to the sizeable graphic arts industry. Its harsh blue light of high actinic value was a perfect match with the requirements of the slow emulsions used in diazo photo-printing processes of the time. It continued as a profitable business, and encouraging results with higher pressure discharges in Europe later re-kindled the interest in mercury lamps for general lighting.

By 1919 the business and technology had developed to the extent that it could no longer be ignored by the giant General Electric Company of America, which bought out the Cooper-Hewitt company. Production relocated from the original factory at 220 West 29th Street in Manhattan, and GE established its own Vapor Lamp Department at the Grand St. premises in Hoboken, New Jersey. As new lamp types continued to be developed in Europe they were quickly adopted at GE's plant and then copied by other American manufacturers. In 1934 an improved Cooper-Hewitt lamp was developed, and it is remarkable that this continued in production at GE's plant until 1965. In the rest of the world the European style medium pressure and high pressure mercury lamps were adopted immediately, and it was only in North America that the antiquated Cooper-Hewitt lamps continued to live on for many more decades.