The invention that Edison is most remembered for is, by far, the electric light bulb. At the age of thirty-one, he decided to focus his energies–and the manpower of the Menlo Park facility–toward creating an electric light system. He began work in the fall of 1878, after returning from a vacation with the physicist George Barker. Barker had encouraged Edison to work on creating an electrical system and discussed ideas with him about it. Edison recognized the staggering potential of an electrical light system and decided to focus on creating one, having just finished work on the phonograph.

At this time, gas lamps lighted most American cities. Other inventors had already done some pioneering work in the electrical light field, especially Humphrey Davy in 1802 (who first produced "incandescence," an electric current flowing through wire) and the Englishman Joseph Swan in 1860 (who produced many experimental incandescent lamps). But no one had been able to completely solve the practical problems of creating an effective and reliable lamp.

From October 1878 until New Year's Day, 1880, Edison developed the components for a lighting system. His experience with telegraph technology assisted him as he tried to envision a system of relays and circuit breakers that would be necessary to making a lamp work. The main problems were locating the proper filament for the incandescent spiral and constructing a lamp that had enough pressure to contain the filament. He perfected new vacuum techniques for the latter problem and rejected the spiral filament in favor of a filament of carbonized thread.

When the lamp with carbonized thread lasted for forty-five hours the staff at Menlo Park realized that they had had a breakthrough. Edison claimed, "none of us could go to bed, and there was no sleep for any of us for forty hours." In November 1879 they tried using carbonized cardboard, and soon they had created an experimental bulb that was superior to any of the others they had tested.

On New Year's Eve, the Menlo Park facility was swarmed by the press, on- lookers, and Edison's financiers, all eager to see the new invention. Edison enthralled the visitors by lighting forty light bulbs all at once, then switching them on and off. The real work, however, consisted in creating a system that was inexpensive and practical: true innovation lay in lighting on a much larger scale, which required generator systems and safety fuse technology.

To develop this system, Edison depended in part upon existing gas lighting systems. He copied the distribution system of gas lighting, which was dependent upon a central power source. During the early 1880s, he set about the complicated research work of developing a system that would light many lamps all at once, without causing electrical fires or damage. This required painstaking work on everything from wire insulators to junction boxes and underground wire mains. His first generators, the "long-waisted Mary Ann" and the "jumbo" weighed hundreds of pounds and produced, in modern terms, only about 100 kilowatts.

Edison's first practical electrical lighting system was established in 1882, on Pearl Street in New York City. It was a central system, designed to provide light to everyone in the area using six "jumbo" generators. On September 4, 1882, the first day of operations at the Pearl Street station, the plant boasted ten 1/2 miles of mains and four 1/2 miles of feeder lines; by the end of the year it served an area of one square mile. By October, the station served over 1,200 lamps.

Edison's work on the light bulb is a good example of how inventors at the time built off of each other's accomplishments and added their own touches to make a product unique. The light bulb was the culmination of nearly a century's worth of work and research on electrical lighting systems, most of it done by other inventors. Edison's contribution to this field was to synthesize all of the past work done on electrical lighting and to solve the lingering problems that had prevented these other inventors from creating a practical system.

The key to Edison's success was his new filament and high-resistance lamp technology. The high-resistance lamps were the result of Edison's attention to Joseph Swan, who had pioneered a low-resistance lamp. Edison's lamp was more practical, because it used thinner, more economical conductors. His discovery of a carbon filament was based upon his work on the carbon telephone transmitter. Here, once again, is a case of Edison using experiments that were not initially successful to spark new inventions.

Edison's savvy business techniques after his invention are also key to understanding why his light bulb became such a phenomenon. His understanding of the marketplace led him to immediately plan for electrical lighting on a large scale; such quick thinking spared him the skepticism of the public about the practicality of an electrical lamp. He also invented his system in such a way as to give the customer choice between the gas lighting system and the electrical system, thereby avoiding the wrath of the gas lighting industry. Their protests would have certainly slowed down his underground wiring plans and possibly kept the Pearl Street station from becoming a reality.

Edison showed foresight not just in planning his Pearl Street station, but also in locating it near an important area in Lower Manhattan: the New York Stock exchange and banking districts. By servicing these areas first, Edison got the interest of the financial world in his electrical system. These interests were able to fund his Menlo Park facility further, allowing him to take on new experiments and expand the electrical lighting system.