gloeidraad

Gloeidraad is the thin wire inside an incandescent lamp that heats up as electric current flows through it, emitting visible light as a result of resistance heating. The filament is typically made of tungsten, chosen for its very high melting point and mechanical strength at high temperatures. In the early days, carbon filaments were used, but tungsten proved more durable and capable of operating at higher temperatures, improving efficiency.

In a traditional light bulb, the gloeidraad is formed into a long, thin length and often wound into a coil or double coil to increase its surface area while allowing a compact bulb shape. The filament is placed inside a glass envelope that is evacuated or filled with an inert gas to reduce oxidation and prolong life. In halogen lamps, a tungsten filament operates in a quartz envelope with a halogen gas, which helps to redeposit evaporated tungsten back onto the filament and extend its life.

Manufacture involves drawing tungsten wire to very fine diameters, attaching it to supports, and shaping it into a stable coil. The lamp design, including filament geometry and the surrounding atmosphere, determines the bulb’s luminous efficacy and lifespan. Compared with modern lighting technologies, gloeidraad-based lamps are less energy-efficient and have largely been displaced in general lighting by fluorescent and, especially, LED sources, though tungsten filaments remain used in some specialty and vintage applications.