Siemens Spherical Tantalum Filament

The emergence of the tantalum lamp resulted from continual efforts to improve the luminous efficacy and life 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.

Siemens' lampmaking operations had until then been restricted almost exclusively to Germany, but the invention of the Tantalum lamp was to shape in very great measure the future of that company as a powerful international force. At first, Siemens sold a license to General Elecric of America to manufacture its own Tantalum lamps. It proved to be a very lucrative deal, with Siemens profiting strongly from its invention. The increased revenue allowed Siemens to expand its own manufacturing base, and in 1908 it set up a factory at Dalston in London, to compete with the British carbon lamp manufacturers.

It is believed that this lamp was produced by the Siemens' British subsidiary. The only marking on this lamp is a letter S etched into the glass bulb - possibly an abbreviation for the name of its manufacturer. It was not uncommon however, for Dalston to manufacture lamps in various other brand names, for its competitors. Rather than licensing the tantalum technology to its British competitors, Siemens retained the production in-house and supplied them to competitors under their own private label.
Manufacturer: Siemens Brothers
Lamp Power: ~54 Watts
Lamp Voltage: ~230 Volts
Lamp Current: ~0.23 Amperes
Cap Type: B22d Large skirted, vitrite
Bulb Type: GA-100 GA-32 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: S-1 Squirrel Cage
Atmosphere: Vacuum Red phosphorus getter
Luminous Flux: Approx 400 lm 32 Candle Power
Luminous Efficacy: 7.5 lm/W 1.7 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: Vertical
Overall Length: 165 mm 6½ inches
Light Centre Length: mm inches
Factory: Dalston England
Date of Manufacture: Approx 1910 Date Code: 67
Original / Present Value: 2s9d (1912) GB £8.59 (2013)
References: 1) Siemens Tantalum Lamp Catalogue, UK, 1912
2) Royal Ediswan Tantalum Lamp Catalogue, UK, 1913