GE Tantalum Filament 25W of American Design

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.
Manufacturer: General Electric Co. of U.S.A.
Lamp Power: 25 Watts
Lamp Voltage: 116-120 Volts 120V nominal
Lamp Current: 0.21 Amperes DC operation only
Cap Type: E26s/25 Brass + vitrite
Bulb Type: SA-58 SA-18 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: S-17 Diamond Cage
Atmosphere: Vacuum Red P Getter
Luminous Flux: 150 lumens 12 CP
Luminous Efficacy: 6 lm/W 2 watts per candle
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: Approx. 1000h on DC 300-500h on AC
Burning Position: Universal
Overall Length: 127 mm 6 inches
Light Centre Length: 83 mm 3 inches
Factory: Central Falls, R.I. U.S.A.
Date of Manufacture: February 1909 Date Code: e11 145
Original / Present Value: Unknown Unknown
References: 1) Networks of Power, T.P. Hughes, John Hopkins University Press, 1993 pp. 167-168.
2) The Making of American Industrial Research, L.S. Reich, Cambridge University Press ISBN 9780521522373 pp. 73-74.
3) The Electric Incandescent Lamp, E.J. Covington, NELA Press, 1998.