Incandescent light bulb
Edison's Menlo Park team tests a carbonized cotton-thread lamp
View full image ↗ How was this image made?
The creative brief sent to the image model. These are instructions, not a record of what actually happened.
Original prompt & settings (JSON) ↗The filament that worked began as six-cord No. 24 cotton sewing thread — and the lamp did not simply burn out: the experimenters deliberately made it brighter until the glass cracked.
Early morning, 22 October 1879
In the early morning of 22 October 1879, Edison and his Menlo Park staff began experiments with straight carbon filaments made from cotton thread. Lampblack spirals had proved hard to form and platinum was expensive; cotton thread was readily available.
Charles Batchelor recorded the procedure: a filament made from six-cord No. 24 cotton thread, attached to platinum wires, carbonized in a closed chamber, then placed in an evacuated bulb to protect it from oxidation.
Fourteen and a half hours
Lit, the lamp produced approximately half a candle of light. Its measured resistance rose from 113 to 140 ohms as it ran — a change Batchelor tentatively blamed on vibration.
After 13.5 hours the staff added battery cells, making the lamp much brighter: at least 30 candles, described as equivalent to three gas jets. The added power overheated and cracked the bulb approximately one hour later, for a total run of about 14.5 hours.
An experiment, and an unsettled anniversary
21 October became the traditional commemorative “Edison Day,” but the laboratory record indicates that the 21st ended without the later-claimed dramatic success, and that Batchelor documented the cotton-thread work on the morning of the 22nd. Institutional summaries remain inconsistent; a National Park Service children's timeline states that newer research invalidates the conventional 21–22 October dating without supplying an alternative date.
What the team had was commercial promise, not a finished product — and not the famous bamboo filament, which became a focus in 1880. Five days later, Batchelor's carbonizing list included cork, fishing line, coconut hair and shell, lampwick, papers, woods, and celluloid.
Sources
Researched 23 Aug 2026 5 sources 3 audit passes Date disputed
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
Date disputed. Sources disagree about when this happened.
What the sources leave uncertain
- October 21 became the traditional commemorative “Edison Day,” but the laboratory record indicates that October 21 ended without the later-claimed dramatic success and that Batchelor documented the cotton-thread experiments on the morning of October 22.
- Institutional summaries are inconsistent: the Edison Papers and Smithsonian historical reconstruction support October 22, while an NPS children’s timeline says newer research invalidates the conventional October 21–22 dating without supplying an alternative date.
- Sources often report either 13.5 or 14.5 hours. The detailed Edison Papers reconstruction explains the difference: the lamp ran 13.5 hours before the team raised the power and approximately one additional hour before the glass cracked.