U.S. Patent 1,025,932
Charles Steinmetz's Metal Halide Lamp
granted on 7 May 1912, shows an attempt by Charles Proteus Steinmetz to improve
the color of mercury vapor lamps by adding halide salts. The lamp used mercury
"pools" as electrodes (labeled "D" in Figure 1), with a
layer of metallic halides on the surface of the pools. ("F" in the
same figure). The problem with this design was that the electrical arc danced
around on the surface of the pool, preventing a consistent color from being
The handwritten notation "1st
action" in the upper left corner is significant. In 1961 GE physicist
Gilbert Reiling filed for a patent on what would become the modern metal halide
lamp. This copy of Steinmetz's patent (among others) was sent to GE in 1962, along with the first of
several rejections by the Patent Office examiner. According to the examiner,
"To use the metal iodides of Beese and Steinmetz in the metal vapor lamp of
Pomfrett would not involve invention."
GE replied that, "the
combination [of these patents] is contrary to the teachings of either and hence
is not a proper combination." In 1964, after a
series of rejections, GE fabricated several lamps according to the
specifications in Steinmetz's patent. They then sent both the replicas and
Reiling himself to Washington, DC. Reiling demonstrated to the examiner that his
lamp operated differently than Steinmetz's, and argued that the new lamp should
receive a patent. Apparently the examiner was convinced, as U.S. patent 3,234,421
was granted in 1966.
In 1996, Reiling donated his original patent document, the copy of Steinmetz's patent seen above, and one of the
Steinmetz replicas to the National Museum of American History. The replica is
currently on display.
The image above has been enhanced electronically.