The Nernst Lamp ELECTRICAL CONDUCTIVITY IN NON-METALLIC MATERIALS

The use of carbon and tungsten filaments mounted in vacuum as early incandescent lamps is well-known, but it is less often realised that an early competitor was Nernst’s ceramic lamp. This made use of the property that , although good insulators at room temperature, many oxides become partially conductive when strongly heated. This is due to the migration of ions rather than electrons, and was commonly considered a deleterious property. Nernst realised however that it might permit the construction of a sturdy incandescent lamp that did not require a vacuum. His early lamps embodied a thin rod of magnesium oxide, initially heated with a coil of platinum wire. Later, he used a modified composition based on zirconia. However, these ‘ceramic’ lamps were unable to compete with a new generation of ‘coiledcoil’ tungsten lamps with filaments mounted in low-pressure argon.