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Broadway lit by Brush lamps in 1881, New York City Trimming a lamp, New York City.

The arc lamp

An arc light produces light by using on electric spark to generate heat between two carbon electrodes causing them to vaporize and burn. Carbon arc lamps saw extensive use throughout the USA and the world from the late 1870s on. Due to their intense light they were not that practical for lighting small interior spaces. However even after the advent of the incandescent bulb, arc lamps survived for decades being used as streetlights and for lighting large interior spaces like factories and mills. Incandescents just didn't have the output of arcs. Today carbon arcs are still used in some large spotlights and projectors.

Arc lamps come from almost the exact historical point when electricity went from being a scientific curiosity to being part of everyday life. This was a time of horse-drawn carriages and gaslights, when the Civil War was just over ten years in the past. For many people an arc lamp was the first electrical device they had ever seen. In the late 1870s a lone arc lamp in a store window (powered by its own little dynamo) could draw large crowds. With electric light came the new dynamos and generators which would spur subsequent electrical development. By the turn of the century electric lights in general were commonplace, and companies like General Electric were making hundreds of thousands of arc lamps a year.

Arc lamp from General Electric Corp, (GE), ca. 1911.

How do arc lamps work? Two carbon rods connected to a current limited source are brought together and then drawn apart. As the carbons separate, a hot ionized path is created between them (the arc) that continues to conduct after the carbons have been separated. This arc burns at thousands of degrees and heats the ends of the carbons to incandescence. Most of the light comes from the tips of the carbons, not the arc itself. As the carbons burn down they need to be constantly adjusted to maintain the proper spacing so that the arc does not go out. The "Brush arc lamp" from GE accomplished this "spacing" issue, and became commercially successful by the late 1870s ushering in the era of electric light.

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Patent Drawing of Edison's Electric Lamp, January 27, 1880.

The lightbulb

On December 31, 1879, Thomas Edison demonstrated his most famous invention: the first practical incandescent electric lamp. He was not, however, the first inventor to experiment with electric light. When Edison began testing possibilities for incandescent lamps, the arc light was already becoming popular for lighting streets, department stores, and other large areas.

	Light Bulb, 1880, invented by Thomas Edison (1847-1931)

Incandescent lamps make light by using electricity to heat a thin strip of material (called filament) so hot that it glows. The color of this glow depends on the temperature, as a blackbody radiator. Many inventors tried to perfect incandescent lamps to "sub-divide" electric light or make it smaller and weaker. These 1878 lamps are examples of less successful versions of the incandescent lamp patented by other inventors before Edison completed his practical lamp in 1879.

Edison tried to find a material that would become incandescent and not melt when heated by electricity. For a long time he tried platinum, but finally he made his filaments by carbonizing a kind of cardboard called Bristol board. In earlier lamps, too much oxygen caused the filaments to burn. Edison acquired the best vacuum pumps so he could empty his bulbs of as much air as possible. Because of this, his carbon filaments did not burn.

Edison's men used vacuum pumps to evacuate electric lamps. Edison also developed an entire system to make electricity and distribute it to many places at the same time. Edison's system included dynamos, switches, electric meters, fuses, distribution lines, and regulators. One of the most important features of Edison's lamp and electrical system was the simple, modern socket familiar to us today.

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