How incandescent light bulbs are made
By the 1970s, just 15 ribbon machines made every incandescent bulb in the world.
- stations
- 7
- things upstream
- 22
- raw sources
- 11
- steps from the ground
- 6
The short version
An incandescent bulb is a glass envelope around a coiled tungsten filament. A ribbon machine blows the glass bulbs from a moving ribbon of molten glass. The filament is drawn from tungsten, coiled, and mounted on a glass stem with lead-in wires. The bulb is sealed, pumped out or filled with inert gas, and capped with a base.
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Blow bulbs from a ribbon
A continuous ribbon of glass rides a conveyor through a furnace. Aligned air nozzles blow it down through holes in the belt into molds below. A typical machine makes 50,000 to 120,000 bulbs an hour.
50,000–120,000 bulbs an hour
Goes in -
Draw the tungsten wire
Sintered tungsten was made ductile in 1906 by William D. Coolidge, so it could be drawn into the fine wire used for filaments.
Goes in -
Coil the filament
The wire is wound into a coil, and in a coiled-coil bulb that coil is wound into a second coil on a mandrel. Coiling packs a long filament into a small space.
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Mount it on the stem
The filament is held on a glass stem with small support wires, and contact wires run through the glass without letting air or gas leak.
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Pump out, fill and seal
The bulb is either evacuated or filled with inert gas to protect the filament from oxidation. Irving Langmuir found that inert gas, nitrogen at first and later argon, doubled the light per watt and reduced blackening.
Goes in -
Cap the base
A base with two or more conductors carries current from the socket to the filament.
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Burn-test the lamp
Bulbs are checked for light and life. Designers trade efficiency against longevity, typically setting life at 1,000 to 2,000 hours for general lighting.
1,000–2,000 hours
Worth repeating
- Less than 5% of the energy a typical incandescent bulb uses becomes visible light, and the rest is released as heat.
- A glowing filament runs at 2,000 to 3,300 K, below tungsten's melting point of 3,695 K.
- By 1939 the Ribbon Machine at Corning was producing 1,000 bulbs per minute, compared with around 150 bulbs per hour blown by hand in the 1880s.
Back to the ground
Follow every input upstream and incandescent light bulb starts as these 11 raw sources.
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Sources
Cite this page: "How incandescent light bulbs are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/light-bulb