Nernst lamp, German, c 1900.
© Science Museum / Science & Society Picture Library
Developed by the German physicist Walther Nernst, the Nernst lamp has a rod of refractory metal oxide which conducts electricity when hot and glows brightly when an electric current pases through it. Up to about 1900 a spirit lamp was used to heat the filament initially, but after that a platinum wire wound round a ceramic spiral was used as a heating element. Nernst lamps were more efficient than carbon filament lamps, but were quickly superseded when metal filament lamps became available.