Research and development facility
Edison's Menlo Park Laboratory, reconstructed at Greenfield Village at
Henry Ford Museum
in Dearborn, Michigan.
Edison's major innovation was the establishment of an industrial research lab in 1876. It was built in
Menlo Park, a part of Raritan Township,
Middlesex County, New Jersey (today named
Edison in his honor), with the funds from the sale of Edison's
quadruplex telegraph. After his demonstration of the telegraph, Edison was not sure that his original plan to sell it for $4,000 to $5,000 was right, so he asked Western Union to make a bid. He was surprised to hear them offer $10,000 ($216,300 in today's dollars.
), which he gratefully accepted.
 The quadruplex telegraph was Edison's first big financial success, and Menlo Park became the first institution set up with the specific purpose of producing constant technological innovation and improvement. Edison was legally attributed with most of the inventions produced there, though many employees carried out research and development under his direction. His staff was generally told to carry out his directions in conducting research, and he drove them hard to produce results.
William Joseph Hammer, a consulting electrical engineer, started working for Edison and began his duties as a laboratory assistant in December 1879. He assisted in experiments on the telephone, phonograph, electric railway,
iron ore separator,
electric lighting, and other developing inventions. However, Hammer worked primarily on the incandescent electric lamp and was put in charge of tests and records on that device (see
Hammer Historical Collection of Incandescent Electric Lamps). In 1880, he was appointed chief engineer of the Edison Lamp Works. In his first year, the plant under General Manager
Francis Robbins Upton turned out 50,000 lamps. According to Edison, Hammer was "a pioneer of incandescent electric lighting".
Frank J. Sprague, a competent mathematician and former
naval officer, was recruited by
Edward H. Johnson and joined the Edison organization in 1883. One of Sprague's contributions to the Edison Laboratory at Menlo Park was to expand Edison's mathematical methods. Despite the common belief that Edison did not use mathematics, analysis of his notebooks reveal that he was an astute user of mathematical analysis conducted by his assistants such as Francis Robbins Upton, for example, determining the critical parameters of his electric lighting system including lamp resistance by an analysis of
Joule's Law and economics.
Nearly all of Edison's patents were utility patents, which were protected for a 17-year period and included inventions or processes that are electrical, mechanical, or chemical in nature. About a dozen were
design patents, which protect an ornamental design for up to a 14-year period. As in most patents, the inventions he described were improvements over
prior art. The phonograph patent, in contrast, was unprecedented as describing the first device to record and reproduce sounds.
In just over a decade, Edison's Menlo Park laboratory had expanded to occupy two city blocks. Edison said he wanted the lab to have "a stock of almost every conceivable material".
 A newspaper article printed in 1887 reveals the seriousness of his claim, stating the lab contained "eight thousand kinds of chemicals, every kind of screw made, every size of needle, every kind of cord or wire, hair of humans, horses, hogs, cows, rabbits, goats, minx, camels ... silk in every texture, cocoons, various kinds of hoofs, shark's teeth, deer horns, tortoise shell ... cork, resin, varnish and oil, ostrich feathers, a peacock's tail, jet, amber, rubber, all ores ..." and the list goes on.
Over his desk, Edison displayed a placard with
Sir Joshua Reynolds' famous quotation: "There is no expedient to which a man will not resort to avoid the real labor of thinking."
 This slogan was reputedly posted at several other locations throughout the facility.
With Menlo Park, Edison had created the first industrial laboratory concerned with creating knowledge and then controlling its application.
 Edison's name is registered on 1,093 patents.
Carbon telephone transmitter
In 1876, Edison began work to improve the
microphone for telephones (at that time called a "transmitter") by developing a
carbon microphone, which consists of two metal plates separated by granules of carbon that would change resistance with the pressure of sound waves. A steady direct current is passed between the plates through the granules and the varying resistance results in a modulation of the current, creating a varying electric current that reproduces the varying pressure of the sound wave.
Up to that point, microphones, such as the ones developed by
Johann Philipp Reis and
Alexander Graham Bell, worked by generating a weak current. The
carbon microphone works by modulating a direct current and, subsequently, using a transformer to transfer the signal so generated to the telephone line. Edison was one of many inventors working on the problem of creating a usable microphone for telephony by having it modulate an electrical current passed through it.
 His work was concurrent with
Emile Berliner's loose-contact carbon transmitter (who lost a later patent case against Edison over the carbon transmitters invention
David Edward Hughes study and published paper on the physics of loose-contact carbon transmitters (work that Hughes did not bother to patent).
Edison used the carbon microphone concept in 1877 to create an improved telephone for
 In 1886, Edison found a way to improve a
Bell Telephone microphone, one that used loose-contact ground carbon, with his discovery that it worked far better if the carbon was
roasted. This type was put in use in 1890
 and was used in all telephones along with the Bell receiver until the 1980s.
It should be noted that the frequency response of the carbon microphone is limited to a narrow frequency range (400 Hz to 4000 Hz), and the device may produce significant electrical noise.
Thomas Edison's first successful light bulb model, used in public demonstration at Menlo Park, December 1879
In 1878, Edison began working on a system of electrical illumination, something he hoped could compete with gas and oil based lighting.
 He began by tackling the problem of creating a long-lasting incandescent lamp, something that would be needed for indoor use. Many earlier inventors had previously devised incandescent lamps, including
Alessandro Volta's demonstration of a glowing wire in 1800 and inventions by
Henry Woodward and
Mathew Evans. Others who developed early and commercially impractical incandescent electric lamps included
James Bowman Lindsay,
Moses G. Farmer,
William E. Sawyer,
Joseph Swan, and
Heinrich Göbel. Some of these early bulbs had such flaws as an extremely short life, high expense to produce, and high
electric current drawn, making them difficult to apply on a large scale commercially.
:217–218 Edison realized that to connect a series of electric lights to an economically manageable size and using the necessary thickness of copper wire, he would have to develop a lamp that used a low amount of current. This lamp must have high
resistance and use relatively low voltage (around 110 volts).
After many experiments, first with
carbon filaments and then with
platinum and other metals, Edison returned to a carbon filament.
 The first successful test was on October 22, 1879;
 it lasted 13.5 hours.
 Edison continued to improve this design and on November 4, 1879, filed for U.S. patent 223,898 (granted on January 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected to platina contact wires".
 This was the first commercially practical incandescent light.
Although the patent described several ways of creating the carbon filament including "cotton and linen thread, wood splints, papers coiled in various ways",
 it was not until several months after the patent was granted that Edison and his team discovered a
bamboo filament that could last over 1,200 hours. The idea of using this particular raw material originated from Edison's recalling his examination of a few threads from a bamboo fishing pole while relaxing on the shore of Battle Lake in the present-day state of
Wyoming, where he and other members of a scientific team had traveled so that they could clearly observe a total eclipse of the sun on July 29, 1878, from the
U.S. Patent#223898: Electric-Lamp. Issued January 27, 1880.
In 1878, Edison formed the
Edison Electric Light Company in New York City with several financiers, including
J. P. Morgan,
 and the members of the
Vanderbilt family. Edison made the first public demonstration of his incandescent light bulb on December 31, 1879, in Menlo Park. It was during this time that he said: "We will make electricity so cheap that only the rich will burn candles."
Henry Villard, president of the
Oregon Railroad and Navigation Company, attended Edison's 1879 demonstration. Villard was impressed and requested Edison install his electric lighting system aboard Villard's company's new steamer, the
Columbia. Although hesitant at first, Edison agreed to Villard's request. Most of the work was completed in May 1880, and the Columbia went to
New York City, where Edison and his personnel installed Columbia's new lighting system. The Columbia was Edison's first commercial application for his incandescent light bulb. The Edison equipment was removed from Columbia in 1895.
Lewis Latimer joined the Edison Electric Light Company in 1884. Latimer had received a patent in January 1881 for the "Process of Manufacturing Carbons", an improved method for the production of carbon filaments for light bulbs. Latimer worked as an engineer, a draftsman and an expert witness in patent litigation on electric lights.
George Westinghouse's company bought
Philip Diehl's competing
induction lamp patent rights (1882) for $25,000, forcing the holders of the Edison patent to charge a more reasonable rate for the use of the Edison patent rights and lowering the price of the electric lamp.
On October 8, 1883, the
US patent office ruled that Edison's patent was based on the work of
William E. Sawyer and was, therefore, invalid. Litigation continued for nearly six years, until October 6, 1889, when a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid.
 To avoid a possible court battle with Joseph Swan, whose British patent had been awarded a year before Edison's, he and Swan formed a joint company called
Ediswan to manufacture and market the invention in Britain.
Mahen Theatre in
Brno (in what is now the Czech Republic), opened in 1882, and was the first public building in the world to use Edison's electric lamps.
Francis Jehl, Edison's assistant in the invention of the lamp, supervised the installation.
 In September 2010, a sculpture of three giant light bulbs was erected in Brno, in front of the theatre.