How Edison’s team at Menlo Park solved the lightbulb problem with a cotton thread

Edison Laboratory (New Jersey)

The first light bulbs were disasters. They lasted minutes, not hours because the filament would burn up or break.

Edison’s crew at Menlo Park tested bamboo, paper, and human hair at his laboratory in New Jersey (say about 3000 materials).

The project alone cost $40,000 (about $850,000 today), funded by profits from Edison’s telegraph and phonograph inventions.

Here’s how Edison cracked the code at his New Jersey lab, now part of Edison National Historical Park where you can walk through his actual workshop.

The Beginning of Failures

Edison built his Menlo Park laboratory in 1876 as the world’s first research center.

He then began studying electric light in 1878. On October 14, 1878, Edison filed his first lighting patent.

By 1879, Edison had gathered 25 skilled workers with expertise in chemistry, math, glassblowing, and machine work.

Arc lamps existed but sparked between carbon rods. Edison first tried platinum filaments because they resisted melting at high heat.

His breakthrough concept was a high-resistance system requiring less power than arc lamps, making household electric distribution possible.

Solving The Vacuum Problem First

A proper vacuum inside the bulb was essential. Without it, oxygen would burn the filaments instantly.

Edison’s team then used a Sprengel mercury vacuum pump, improving its design to remove nearly all air.

Their system combined a Geissler pump for initial air removal followed by a Sprengel pump for final extraction.

This vacuum technology achieved pressures below one millitorr, allowing filaments to glow for hours instead of seconds.

Testing Countless Materials

Edison’s team tested over 1,600 materials between 1878 and October 1879 with a focus on high-resistance filaments.

They carbonized most materials by heating them until only carbon remained, creating better heat-resistant conductors.

Charles Batchelor documented each experiment, recording twenty different carbonized materials tested on October 27, 1879 alone.

The Cotton Thread Insights Proved Useful

On October 21, 1879, Edison’s team used ordinary six-cord cotton thread, 0.013 inches thick, as a filament.

Workers first carbonized the thread by heating it without oxygen, creating a carbon fiber. They then mounted it inside a glass bulb with platinum wires.

The assembled bulb, connected to vacuum pumps, which spent hours removing all air, preparing for the critical test.

The Historic Night of the Light Bulb

On the evening of October 21, 1879, the cotton thread glowed with soft orange light when electricity flowed through it.

The bulb started with 113 ohms of resistance, rising to 140 during use. Powered by 18 battery cells, it gave off light equal to half a candle.

Team members took shifts watching the bulb throughout the night.

Unlike earlier attempts where filaments flickered or burned out rapidly, this cotton thread maintained steady illumination.

Thirteen And A Half Hours Made a Difference

The carbonized cotton filament continued glowing until it finally burned out after 13.5 hours. Increasing the power boosted brightness to equal three gas jets.

Previous attempts with other materials typically lasted minutes. This duration marked the threshold of practical lighting for homes and businesses.

Success shifted the lab’s focus from questioning if incandescent lighting could work to making filaments last longer.

The team often worked around the clock, taking meals and brief rests at the laboratory during critical testing periods.

The Men Behind The Light Bulb Success

Charles Batchelor, Edison’s English-born chief assistant, documented experiments and provided mechanical expertise.

Francis Upton contributed mathematical knowledge from Princeton, calculating electrical resistance and power requirements.

John Kruesi, the Swiss-trained machine shop foreman, turned rough sketches into precision experimental apparatus.

William Joseph Hammer joined in December 1879, focusing on bulb testing and later managing the first commercial lamp factory.

From Experiment To Patent Revelations

Edison filed a patent on November 4, 1879, describing “a carbon filament or strip coiled and connected to platina contact wires.”

In November and December, the team refined the bulb, and by year’s end, improved versions burned for 40 hours, making commercial use practical.

The U.S. Patent Office granted Edison patent #223,898 on January 27, 1880, protecting this valuable invention against fraud.

Demonstrating the Lighting System

Edison went public on New Year’s Eve, 1879, at Menlo Park, declaring, “We will make electricity so cheap that only the rich will burn candles.”

The Pennsylvania Railroad also ran special trains bringing hundreds of visitors and reporters from New York City.

Over 3,000 people witnessed the demonstration of the soft, steady glow, unlike any lighting they had seen before.

Newspaper coverage transformed electric lighting from a laboratory curiosity into a highly anticipated consumer product.

Going Beyond The Laboratory

In 1880, Edison converted a Menlo Park building into a lamp factory and installed the first commercial system on the steamship SS Columbia in May 1880.

With J.P. Morgan’s financial backing, Edison formed the Edison Electric Light Company to manufacture lamps and build power systems.

The Pearl Street Station opened in Manhattan in 1882, providing electricity to 59 customers and proving centralized power generation worked.

According to the National Grid, Edison’s invention led to the first U.S. commercial power plant and launched the electric utility industry.

Visiting Edison Laboratory Today

Visit the Thomas Edison Center at 37 Christie Street, Edison, NJ 08820, open Wednesday through Sunday, 10 am to 4 pm.

Admission costs $7 for adults, $5 for seniors, and $3 for children ages 6-17, with free entry for children under 6.

The site includes a museum with original artifacts, interactive displays, and a film, plus the Edison Memorial Tower topped by a giant light bulb.

To get there, take NJ Turnpike Exit 10 and follow the signs for Edison/Menlo Park, with free parking available onsite.

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