Early Light Bulbs
Early Light Bulbs
The warm glow of the light bulb is the part of today’s electric lighting system that we know best. Thomas Edison is often said to have invented the light bulb, but his bulb was not a completely original idea. In fact, the principle of electric incandescent lighting (making a wire glow by sending electricity through) had been around since at least 1802, when Englishman Humphry Davy demonstrated it. In 1820 another English inventor, Warren De la Rue, used a platinum filament inside a glass bulb, an idea Edison would later try but reject. The air inside the De la Rue bulb was pumped out, because inventors understood that if the filament was not in a vacuum, the oxygen in the air would cause a chemical reaction with the filament and destroy it. One problem with doing things this way, however, was that it was difficult to seal the glass around the wires that supply electricity to the filament. Finding a good material for the filament and keeping the air out were major problems Edison eventually overcame.
De la Rue’s platinum bulb worked, but platinum was far too expensive to use in commercial light bulbs. Thomas Edison, after investigating many different filament materials, settled on carbon filament in 1879. At about the same time, an English inventor named Joseph Swan came up with almost the same idea, leading to claims that it was he who really invented the light bulb. Clearly, no single inventor deserves sole credit for the light bulb. What was unique about Edison’s work was that he carried the idea from laboratory to commercialization, taking into consideration not only technical problems, but also issues like economics and the production of bulbs.
Edison’s carbon filament gave his lighting system an inexpensive bulb, and also the carbon filament worked well at about 110 volts, which Edison considered an economical and safe voltage for the distribution of electricity. In the original Edison and Swan bulbs, the filament was made by burning a cotton thread until all that was left was black carbon. However, the resulting filament was fragile, so Edison later substituted a burned bamboo filament (another idea that had been tried earlier). Combined with the use of an improved vacuum pump to clear more air out of the bulbs, this gave his lamps a maximum lifetime of approximately 1200 hours, versus only 14 or so for the cotton filament bulb.