Incandescent lamp with tantalum filament

By the late 1890s, carbon filament lamps were no longer the hand-made devices demonstrated by Thomas Edison. He and many others had refined them into mass-produced, reliable products. But the energy efficiency of carbon lamps remained poor, leading researchers—especially in Europe—to seek better filament materials. In 1902 Germans Werner von Bolton and Otto Feuerlien invented a filament made from element number 73, tantalum. Tantalum lamps produced 5 lumens per watt (lpw), much better than the 3.2 lpw of the carbon lamps of that day.
The electrical resistance of tantalum was lower than carbon, though. In order for the total resistance of a tantalum lamp to match the total resistance of a carbon lamp, it had to have a much longer filament. In order to support the longer filament inside a bulb of reasonable size, von Bolton and Feuerlien used a series of hooks attached to the lamp's central glass stem. The filament wound up and down within the bulb. Though the design looked complex, it worked well and was later adopted for the tungsten filaments that replaced tantalum around 1910.
This particular lamp was made by the inventors' employer, Siemens and Halske. Tantalum lamps became the first metal filament lamps offered for sale in the U.S. and in 1909 became the first lamps to carry the trade-name Mazda.
Lamp characteristics: Brass medium-screw base with skirt and porcelain-dome insulator. A tantalum filament with 11 upper and10 lower support hooks. The support hooks are angled in order to keep tension on the filament, which tended to sag during operation. The stem assembly features soldered twist and crimp connectors, a Siemens-type press seal, and a cotton insulator. Tipped, straight-sided envelope.
Date made
ca 1907
date made
ca. 1907
Siemens & Halske
Physical Description
tantalum (overall material)
glass (overall material)
brass (overall material)
porcelain (overall material)
cotton (overall material)
overall: 12 cm x 6 cm; 4 3/4 in x 2 3/8 in
ID Number
catalog number
accession number
Credit Line
from General Electric Company
See more items in
Work and Industry: Electricity
Energy & Power
Data Source
National Museum of American History


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