20th Century Inventors:
Metal Halide Lamps
S.I. Negative #99-4126,
© General Electric
Gilbert H. Reiling, 1962
demonstrating an experimental metal halide lamp
"I knew what the lighting goals were, everybody wanted more efficiency, and they wanted white light, and they wanted something economical."
-- Gilbert Reiling, 1996 interview
The high intensity mercury-vapor lamp, introduced in 1932, quickly replaced carbon
arc lamps in exterior applications. Despite a somewhat poor blue-green color,
mercury-vapor's 40 lumens per watt was double the efficacy of incandescent lamps and
required much less maintenance than carbon arcs.
Many attempts were made over the years to improve the color of the mercury
discharge. One method tried in 1912 by Charles Steinmetz involved adding metallic
elements to the mercury, often in the form of salts or "halides." By the early 1950s,
experiments in Germany by Otto Neunhoeffer and Paul Schulz showed promise though
their work apparently did not result in a commercial product at that time. Toward the end
of the decade, Bernhard Kühl and Horst Krense began building on this earlier work
and filed for a West German patent in August 1960.
In 1959, Gilbert Reiling at General Electric's Schenectady Research Lab began
working on the thermodynamics of the mercury discharge. By June 1960 he reported to
lab management that he had made lamps with "twice the luminous output" of a standard
400 watt mercury-vapor lamp and "with a white color which appears more pleasing to
the eye." His lamps contained various mixtures of sodium-iodide and thallium-iodide.
GE began an intensive development program, and announced a commercial metal
halide lamp in 1962.
The photo is a public relations shot taken by GE for the 1962 announcement.
Notice that the lamp is only an arc-tube -- it has no glass envelope such as you would
see on a lamp in the field. An important function of the glass envelope is to block
ultraviolet light produced in the arc-tube. Posing for this photo could have resulted in
sun-burns for Reiling (and for the photographer), but Reiling recalls that they worked
fast so as to avoid this.