Cooper Hewitt mercury vapor lamp

Many inventors worked to improve incandescent lamps during the 1890s, but only a few tried to develop practical discharge lamps. Unlike incandescent lamps that make light by heating a filament until it glows, discharge lamps make light by passing an electrical current through a gas. The current energizes the gas which then emits light. One inventor, Peter Cooper Hewitt, achieved success with a discharge lamp using mercury.
Hewitt experimented with mercury-filled tubes in the late 1890s and found they emitted an unappealing bluish-green light. The amount of light given off, however, was startling. In 1902 the Cooper Hewitt Vapor Lamp Company (backed by George Westinghouse) was established to make the lamps. Though few people would want his lamps in their homes, Hewitt realized that the poor color would not matter for other uses. Photo studios used Cooper Hewitt lamps extensively. In an age of black and white film, the color of a photographer's light made little difference--they just needed lots of light. Industrial uses for the lamp also emerged.
Ultimately, Cooper Hewitt lamps proved cumbersome. A heavy ballast was needed to control the electrical current and each lamp contained nearly 1 pound of mercury. Starting early models required the user to tip the entire fixture over so that the mercury would run from one end to the other. Tungsten-filament incandescent lamps made in the 1910s provided almost as much energy efficiency as Cooper Hewitt tubes and gave a much better color. General Electric bought the Cooper Hewitt Company in 1919, and in 1933 began marketing a more convenient mercury lamp, the H-1. The H-1 and fluorescent lamps used only a fraction of the mercury found in Cooper Hewitt lamps, but produced light much more efficiently.
This unit is a production-model Cooper Hewitt lamp from about 1904. An attached manufacturer's tag (not shown) gives proper operating positions for various models, and includes a caution notice and a six month warranty.
Lamp characteristics: Glass, U-shaped tube with bulbs at both ends. Bulbs house mercury-pool electrodes. A single brass screw contact is mounted on the smaller bulb; two brass screw contacts are on the larger bulb. The tube is attached to a mounting bracket that holds it in its fixture. Pads of asbestos insulation keep the glass from direct contact with the metal bracket. Unit contains about 1 pound (.5 kilograms) of mercury.
Date made
ca 1904
date made
ca. 1904
Cooper Hewitt Electric Company
Physical Description
mercury (overall material)
glass (overall material)
metal (overall material)
overall: 26 1/2 in x 7 1/2 in x 3 1/2 in; 67.31 cm x 19.05 cm x 8.89 cm
ID Number
catalog number
accession number
Credit Line
from Osram Sylvania Inc., thru Richard H. Dowhan
See more items in
Work and Industry: Electricity
Energy & Power
Data Source
National Museum of American History


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