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U.S. Patent 1,025,932
Charles Steinmetz's Metal Halide Lamp

Image of Charles Steinmetz's metal halide patent, 1912

This patent, 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 generated.  

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.


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