How Does A Light Bulb Work?

A guide to the function of light bulbs, including insights into the history and science this household device.

A light bulb is a device for the conversion of electrical energy into visible light. The first practical light bulb was invented by Thomas Edison at his Menlo Park laboratory. Prior to this there was electric light available, but only electric arc lights, which had many problems. Edison's goal in making his own electric light was to create a light that was safe, cheap, and would not cause the whole circuit to fail with the failure of one light. The arc lights available when Edison began work on his own electric light were wired in series, so the failure of any one of them would cause the whole circuit to fail.

When current passes through a modern light bulb, it goes through a series of connectors set up to deliver the current to a carbon-based filament in the center of the bulb. This filament has a high resistance to electric current, so, as the current passes through it, the filament heats. Soon the filament is so hot it begins to glow - this is called incandescence, and it is where the light from an incandescent light bulb comes from. So long as current keeps going through the filament it is kept hot enough to keep glowing providing the light with which we are so familiar.

The single biggest difficulty that Edison faced while working to develop his incandescent light bulb was finding a filament that would be three things: first it had to display the proper incandescent properties - without that it was just a fancy resistor that didn't do anything worthwhile; second it had to be cheap enough to mass produce - several of Edison's early filaments would incandesce quite well, but the use of platinum filaments would have been prohibitively expensive; finally it had to last for a reasonable period of time - a filament that burned out after 10 or 20 hours of use would be of only limited appeal to the consumer, no matter how safe or bright it might be.



Eventually after testing several thousand different materials for the desired properties Edison settled on the carbon fiber that his assistant Latimer had formulated. Eventually Latimer created a process for the mass manufacture of his filament. The first light bulbs were good for about 50 hours of incandescence, but advances in the filaments have progressed so that Edison found a filament that would provide light for 1200 hours, and today the average life of an incandescent bulb is about 1500 hours.

The modern incandescent bulb no longer uses Latimer's carbon fiber, but a coiled tungsten wire as the light emitting filament. Coatings on the inner surfaces of the bulb also makes for a more "˜gentle' or "˜soft' light than the original bare bulbs provided. However the modern incandescent bulb remains only a series of incremental improvements on Edison's original.

There is some room for controversy about the true inventor of the incandescent bulb. The original incandescent light bulb was displayed by an English scientist by the name of Swan in 1860. The problem was that Swan's 1860 bulb didn't have a strong enough vacuum to last very long, and his batteries weren't strong enough to produce sufficient current to actually generate incandescence. In 1875 he returned to the idea of the incandescent light bulb, and produced a working prototype in 1878. His light bulb, according to some, was the model that Edison copied to produce his own light bulb. Swan may have invented the incandescent light bulb, even to using a carbon fiber, it is Edison who first produced a commercially viable product, hence the hedge at the beginning of this article about Edison inventing the "˜practical' light bulb.

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