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The differential arc lamp, 1878

1878: The differential arc lamp

With the differential arc lamp of 1878, Siemens brought electric light to streets and plazas, thus also helping expand the delivery of electricity. In continuous competition with gas lighting, electric light slowly proved its worth in urban centers, initially with the arc lamp and then with the incandescent-filament lamp.


But in carbon arc lamps, the inevitable burn-down of the electrodes, which increased the distance between them, ultimately caused the arc to burn out. So the electrodes had to be adjusted constantly by hand – a complicated procedure for routine operation.


True, Werner von Siemens had already discovered the principle of differential regulation in 1873. But Siemens chief designer Friedrich von Hefner-Alteneck was the first to embody it in a design, in 1878. He invented an automatic control that autonomously adjusted the carbon rods so that the burned-out electrodes had to be replaced only occasionally. And now several arc lamps could be run from a single generator, where previously each lamp needed a generator of its own – a major step in the direction of general electric lighting.

Street lighting in Berlin, 1882

1882: The first permanent street lighting in Berlin

Siemens brings light to darkness: The Berlin Industrial Exposition of 1879 saw the first series-connected differential arc lamps, powered only by a single dynamo. They were installed in the city's Kaisergalerie, a shopping galleria based on models from Paris and Brussels, now in the Mitte district of town. After this successful test, in 1882 Siemens got the order to install Berlin's first permanent electric street lighting on Potsdamer Platz and Leipziger Strasse.


This was followed by railroad stations, office buildings, factories and port facilities. It was the beginning of Germany's large-scale use of arc lighting. In 1888, finally, Berlin's grand Unter den Linden avenue was illuminated by 108 lamps.


Even though the investment was three times what it would have cost to improve the existing gas lighting, many municipalities decided on electric light. Yet the conflict between gas and electricity continued for several decades more, until electric street lighting finally won out.


Because it was so large, and its light was too brilliant for home use, the differential arc lamp was gradually replaced by the incandescent-filament lamp.

The tantalum lamp, 1905

1905: Tantalum lamp

What would be the right filament for light? Werner and his son Wilhelm were already interested in the problem back in 1882. As they experimented looking for a suitable incandescent filament lamp, they first tried metal wires, but soon moved on to carbon filaments – which they did in grand style. Because that same year, Siemens built the first incandescent-lamp factory in Germany, producing the first Siemens carbon filament lamps.


But the investigators weren't satisfied. Wilhelm asked Werner Bolton to search for a better filament. It was Bolton who discovered that tantalum was a metal with all the desirable characteristics for conducting electric light. It has a high melting point (around 3,000 degrees Celsius), a low vapor pressure, and easy deformability. Ideal conditions for replacing fragile carbon filaments with a stable metal filament. In 1905 – some 20 years after the first experiments – Siemens presented its customers with the first commercial metal-filament lamp, the tantalum lamp.


Siemens had bet on the right horse. In the coming years, the tantalum lamp would become one of the company's biggest sales drivers. By 1914 Siemens had sold more than 50 million lamps worldwide. These lamps continued to be made in the USA, England and France even after World War I began, with filaments always provided by Siemens.