Incandescent Light Bulbs
October 22nd marks the anniversary of Thomas Edison’s successful test of his prototype for an incandescent light bulb.
Although Thomas Edison is often credited with the invention of the incandescent light, that discovery actually belongs to Sir Humphrey Davy, who in 1802 passed an electrical current through a platinum filament to make it glow. Davy chose a platinum filament because of its high melting point, but it did not glow very brightly or last very long. Those observations were the first indicators that finding a suitable filament for an electric light would be a significant challenge.
Because the thin, threadlike wire filaments offered high resistance when electrical current was passed through them, they tended to burn out rapidly, making platinum impractical for widespread long term use. Having tested a number of metals including platinum, Edison used carbonized cotton thread for the filament in his experimental light bulb, and building on the work of British physicist and chemist Joseph Swan, he also created a vacuum inside the bulb so that fewer air molecules were present to react with the filament. Edison’s success resulted in part from judicious use of others’ experimental results, but even more from his access to superior equipment. Both his pump that was able to pull a higher vacuum than others and the high energy power source he built to provide electricity contributed to the successful test of his carbon filament incandescent light bulb on October 22, 1879.
The subsequent development of the tungsten filament in 1904 by Hungarian Sándor Just and Croatian Franjo Hahaman is looked upon as one of the greatest contributions to light bulb technology because the tungsten wire is inexpensive to produce and lasts much longer than platinum or carbon. The fragility of the tungsten filament, which may be broken accidentally even if the glass bulb remains intact, is offset by its high melting point and strength at high temperature. Tungsten’s glow is significantly stronger than that of a carbon or platinum filament, and it was found that filling the light bulb with inert gases nitrogen and argon made the light even brighter to the point that the inside of many bulbs is coated with silica to remove the glare from the glowing unshielded filament.
Although we are gradually moving away from incandescent bulbs toward more energy efficient light sources, on this anniversary of Edison’s test, it is appropriate to shed a little light on the history of this important invention.
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