Drahtfilaments

Drahtfilaments, or wire filaments, are thin metallic conductors used as the light-emitting element in certain electric lamps and vacuum tubes. When current passes through a filament, it heats rapidly and emits light by incandescence. The term typically refers to tungsten filaments in modern incandescent lamps, though carbon filaments were common in early devices.

Materials used for Drahtfilaments include tungsten, chosen for its very high melting point, low vapor pressure at operating temperatures, and ductility when drawn to fine diameters. Earlier filaments relied on carbon, while some specialty applications use tantalum or tungsten alloys to achieve specific performance traits. In halogen lamps, tungsten filaments operate within a halogen cycle to extend life.

Design and operation: Drahtfilaments are formed from extremely fine wire, often coiled into a helical or double-helix shape. The coil increases electrical resistance and surface area, allowing practical operating temperatures at manageable currents. Filaments are mounted on heat-resistant lead wires and supported by glass or ceramic stems inside the bulb. In vacuum or inert gas environments, tungsten evaporation is minimized; halogen lamps use the chemical cycle to recycle evaporated tungsten.

Manufacture and testing: Production involves drawing tungsten to micron-scale diameters, annealing to improve ductility, forming coils, assembling on a support structure, and sealing into the glass envelope. Filaments undergo aging tests to detect premature failures and to ensure uniform resistance.

History and applications: Tungsten filaments enabled practical incandescent lighting in the early 20th century, replacing carbon filaments. Today, incandescent lamps are less common due to efficiency standards, but Drahtfilaments remain in decorative, stage, and certain high-temperature applications, and are also used in some vacuum tubes as heater elements.