||The emergence of the tantalum lamp resulted from continual efforts to improve the luminous efficacy and lifetime of the incandescent lamp, and its invention is credited to Dr. Werner von Bolton and Dr. Otto Feuerlein of the Siemens & Halske laboratories in Berlin-Moabit. Although their first lamp was created in December 1902, it was not until 1905 that production commenced. The reduced vapour pressure of tantalum, by contrast with carbon, permits higher temperature operation for the same lamp life. This yields an efficacy of about 6 lm/W, double that of the carbon filament.
Soon after the launch of the tantalum lamp in Europe, news of the breakthrough caused great concern at GE, who together with National had operated a near-monopoly of the American lamps market since 1901. Siemens & Halske offered GE the American rights to the tantalum lamp in 1904 for a high price, but GE declined owing to its unsuitability for use on AC circuits. However such was the level of the threat that GE eventually conceded, and on 10th Feb. 1906 for a payment of $250,000, secured the American rights for itself and National to produce the lamps on a royalty basis. All of the American-made lamps were produced with tantalum wire sourced from Berlin.
This situation caused enormous stress within GE, because its research laboratory had been established precisely to maintain a leadership position which would avoid paying competitors for the use of lighting-related patents. Effort intensified on finding a filament to surpass tantalum's restriction to DC, and by 1907 success was achieved with the sintered tungsten filament. However its high price meant that tantalum production continued until 1913, after which Coolidge's development of ductile tungsten entirely displaced it from the USA market.