tungstenfilament

Tungsten filament is a thin wire of tungsten used in incandescent light bulbs and other high-temperature lamps to convert electrical energy into light and heat. Tungsten's exceptionally high melting point (about 3,422°C), high tensile strength, and relatively low vapor pressure at operating temperatures make it well suited for prolonged high-temperature operation. When a filament is heated by electric current, it glows white-hot and emits a broad spectrum of visible light.

Filament construction uses tungsten wire drawn to a very small diameter and formed into a tight coil or spring-like shape to increase electrical resistance and surface area. The coiled configuration also improves mechanical stability and reduces sagging when hot. The filament is supported inside a vacuum or inert-gas-filled glass bulb by low-melting-point metal leads (often molybdenum or tungsten) that pass through the glass and connect to external contacts.

Operation and life: The filament is typically heated to temperatures of roughly 2,500–3,000°C. A bulb is evacuated or filled with an inert gas to slow tungsten evaporation, which would thin the filament and shorten life. Historically, small amounts of dopants such as oxide additives were used to improve electron emission, but modern general-service bulbs rely on the inert environment and filament purity to extend life. Filament life is limited by tungsten diffusion and evaporation, mechanical fatigue from thermal cycling, and degradation of support structures.

History and significance: Tungsten filaments replaced carbon filaments in the early 20th century after developments that produced ductile, high-purity tungsten, notably the Coolidge process. This enabled longer-lasting, more efficient incandescent lamps and helped accelerate widespread electric lighting until alternatives such as LEDs emerged.