Thomas Edison: Invention Of The Lightbulb
Thomas Edison, known by everyone as the "Wizard of Menlo Park," thought the electric lightbulb would be easy to invent. It wasn't.
The modern electric light bulb consists of a glass bulb with a slight vacuum of argon gas which supports a filament of wound tungston wire, but it took many years of experimentation to arrive at the right formula.
Thomas Edison got the process started, but it took him much longer than he anticipated to get a working model. In 1878, when Edison got started, he was so sure that this was going to be easy, he collected money from the Vanderbilts and J.P. Morgan to form the Edison Electric Light Co. before he had hardly begun. A year went by, and Edison still didn't have a workable model. Big money gets impatient quickly. Edison was embarassed and frustrated.
At first blush, it seems like a very simple problem. Take two wires from a power source and run them through a glass bulb. When you balance the amount of power against the thickness of the wire, the bulb should glow and make light. Simple. So why didn't Edison's experimental bulbs work?
Basically, a lightbulb is always burning up. In ordinary atmosphere, as you increase the power that goes through a wire, it starts to lose its density and the wire breaks. The old-fashioned camera flashbulb newspapermen used to use in 1940s movies did this on purpose. Too much juice is forced through too fine a wire network, and the bulb flashes but immediately burns out.
If you want a light to remain on for more than a few minutes, you need to take the oxygen out of the atmosphere and replace it with an inert gas such as argon which does not encourage burning. Edison tried all kinds of gasses and all kinds of vacuums, but he couldn't get the balance right. If you want the wire to glow with heat, then you need a wire which is hard enough not to disintegrate under heat stress. Tungston reaches 4500F inside a modern lightbulb, but it doesn't burn out because the argon, together with a slight vacuum, won't let it.
Sometimes Edison got a bulb that would light for several minutes but not give off much light. Sometimes the bulb exploded in a flash. Sometimes, it just remained dark and let the current pass right through it.
If you take a close look at a modern ligh bulb, you will see that the wire inside the bulb actually consists of tiny coils of wire so small you can hardly see them. The length of that wire regulates the Wattage or candlepower intensity of the bulb. At first Edison just put one strand of wire in the bulb, but the light it gave off was way too little to matter. Lengthening the wire intensified the light.
Edison's original idea came from an arc light he saw demonstarted in Connecticut, so he settled on using lamp black carbon on his filament. He sent his assistants all over the world to find possible filament materials. At great expense, they brought back more than 6000 natural materials which Edison worked into his experiments alone or in combination until he found that high carbon on an intensely wound cotton thread seemed to do the trick.
For years the Edison Light Company continued to improve the lightbulb until some unknown date, when someone discovered planned obsolescence, and they started to work on manufacturing a lightbulb which would last for less time.