Nernst lamp, c 1900.
© Science Museum / Science & Society Picture Library
Lamp 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. Nernst lamps were more efficient than carbon filament lamps, but were quickly superseded when metal filament lamps became available.