On this day in 1879, Thomas Edison first successfully tested an incandescent light bulb. We celebrate his success as one of the great inventions of history, but Dr. Boli believes that we completely miss the point of it. Herds of inventors were working on incandescent light bulbs, all following the same notion of putting a filament in a vacuum; Edison himself faced years of patent litigation from other experimenters who claimed to have come up with his idea first. If he had not succeeded in 1879, someone would have succeeded in 1880.

It is at the other end of his bulb that we see Edison’s real genius. When Alexander Graham Bell gave us the telephone, it was an appliance that had to be installed in the home by a professional telephone-company technician. It was not until the latter twentieth century that a connector was devised to make it possible for anyone to plug in a telephone. Another inventor might have given us light bulbs, but they would probably have been light bulbs that had to be installed by your electric company’s technicians. Edison saw that the secret to making electric lighting a success was to make it possible for the ordinary consumer to install the bulbs. Thus the Edison screw mount was born, a connector so simple that the simplicity of its operation has become a standing joke. Even when other connectors are used—the English bayonet mounts, for example, or the two-pin connector promoted by Westinghouse—they followed Edison’s design philosophy, while changing the design itself enough to escape his patent. The screw-mount connector is such a success, in fact, that it will survive the demise of the incandescent light itself: compact fluorescents and LED bulbs are successful only because they use the same connector.

The next time you see a light bulb used in a cartoon as an image of a bright idea, remember at which end of the bulb the genius really lies.


  1. Captain DaFt says:

    Actually, Edison’s only invention that he created himself that wasn’t simply a variation of existing products was Menlo Park.

    There he gathered the brightest inventors he could pay almost nothing (They were bright innovators, but not very bright financially), and told them what to create, then claimed the patents for himself.

    His only contribution to the light bulb, aside from telling his staff “Build me one”, was to doze in front of the prototype until it burned out.

    Several inventors came up with similar designs, some several years before Edison, but he had the lawyers and cash to beat them all in court, save one.

    Joseph Swan’s bulb was patented before Edison’s, and he had the resources to beat Edison in court, so Edison struck a deal with him.

    Edison took the credit in the USA, Swan took credit in England, and their combined resources beat down all other inventors in court.

    Truth is, neither’s bulb on its own would have been successful due to a major flaw; the vacuum being broken due to leakage between the glass and the leads to the filament. This limited the lifespan of the Bulbs to a couple of days on average.

    It took another inventor’s design, a wax with very low vapor pressure, and very high melting point, to make the light bulb practical. This is used to seal the metal screw cap to the bulb’s glass, even today.

    These days an alloy is also used for the leads to the filament, that has the same thermal coefficient of expansion and contraction of glass, to maintain the vacuum seal.

    Also worth noting; the modern bulb has a partial vacuum. since a bit of inert gas is added to keep the filament from evaporating and blackening the inside of the bulb.

    Edison was a genius at self promotion and litigation, to the point that when his son started promoting his own business in batteries, Edison took him to court and forced him to change his last name.

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