Electric lighting

An incandescent lamp makes light the way a poker in a fire does: heat any solid hot enough and it glows, first dull red, then orange, then white. The problem is that almost anything hot enough to give useful light will burn or melt in ordinary air. The lamp solves this two ways at once. It uses a filament of high resistance so a modest current heats it fiercely; and it seals that filament inside a glass bulb from which the air — and so the oxygen — has been pumped out, so the filament can sit at white heat for hundreds of hours instead of flashing to ash. Carbon was the first filament material that worked; tungsten replaced it after 1906 because it tolerates far higher temperatures and so glows brighter and whiter.

Until this, artificial light meant an open flame — a candle, an oil lamp, a gas jet — each of which consumes oxygen, throws soot and heat, and threatens fire. Electric light burned nothing in the room. It could be switched on from across the house, multiplied to thousands of identical points from a single wire, and left unattended. It broke the tyranny of sundown over factories, libraries, streets, and homes, and it did so cleanly enough to belong indoors by the hundred. The lit city and the round-the-clock workplace begin here.

The idea of glowing a wire was old; making it last was the whole battle, and it was won on two fronts. Joseph Swan in England had a working carbon lamp in principle by 1860 but was defeated for years by bad vacuums — without a hard vacuum the filament simply burned out. The Sprengel mercury pump of the mid-1860s (Sprengel's 1865 pump) finally gave the vacuum he needed; his first public demonstration in Newcastle in December 1878 failed when the lamp burned out, but he showed a working carbon lamp there in early 1879. In America, Thomas Edison's Menlo Park team attacked the same problem systematically, testing thousands of filament materials, and on 22 October 1879 ran a carbonised-cotton-thread lamp for 13.5 hours. Edison's particular contribution was the reasoning behind the *high-resistance* filament: a thin, high-resistance strand could be lit with little current, which meant thin, cheap distribution wires and many lamps wired in parallel — the difference between a laboratory curiosity and a service you could sell to a whole street. He filed his lamp patent (US 223,898) on 4 November 1879 and built the generating stations to feed it.

The bulb was only the visible tip of a system. To sell light, Edison had to build the rest — central generating stations (Pearl Street, New York, 1882), meters, sockets, switches, fuses, and distribution mains — and in doing so he created the model of electricity as a metered utility piped to every building. That grid, once laid for lighting, became the delivery network for everything electric that followed: the motor, the appliance, the radio, the computer. And the demand for a *better* filament pushed materials science toward tungsten and the drawn-wire industry, and eventually toward the fluorescent tube and the LED that have now largely replaced the glowing wire that started it.