In the midst of dynamos, meters and electromagnets of the Edison exhibition at the National Museum of History and Technology hangs a picture of Sir Joseph Wilson Swan (1828-1914), who invented an electric light bulb -- one year before Thomas Edison.

Like Edison, Swan used a carbon filament that glowed in a vacuum without burning or melting. The difference between Swan's way and Edison's is that you had to turn on a dozen or more lights at once to turn on one of Swan's. Swan sued Edison for patent infringement, but an English court decided there was a crucial difference between the two inventions: Edison's was practical.

Practicality was the key to Edison, explained Bernard Finn, the Smithsonian's curator of electricity, at the press preview of the exhibit "Lighting a Revolution," which opens today. Subtitled "The Birth of Electric Power," the show focuses on the role of the humble, taken-for-granted light bulb as the link that brought the world out of the age of steam and into the age of electricity.

The personality of Edison dominates the show, which includes blownup photographs, cartoons, copies of his publications, relics of his laboratory and even a Fox Movietone newsreel showing the hard-of-hearing, 82-year-old inventor at work in his laboratory while associates wander in to shout information into his right ear.

"Thomas Edison was not really a scientist, but he was a great inventor," said Finn, who organized the show. "And unlike most inventors of his time, he did it because he thought it was fun. He would develop an invention and then plow the profits back into his laboratory so that he could invent something else.

"He gathered around him some very talented associates, and once he had the capital, he arranged it so that whatever he might need was available instantly. cIf he needed a glass bulb, there were glass blowers sitting around waiting for an order. It was very expensive, but Edison could get what he wanted in a few minutes, while other inventors might have to wait for weeks or months."

Edison was as much an entrepreneur as an inventor, and had a track record that was a magnet for inventors. The Edison Electric Light Co. was established a year before he actually produced a workable light bulb. "It was a supreme gesture of confidence," according to Finn, "and also very practical. He started a company to sell electric light bulbs before he had an electric light bulb.

"Then he used the money from the company to develop the bulb. From there, it was a natural step to set up the power station on Pearl Street in lower Manhattan. That was in 1882, by which time the first primitive bulb had developed into a form that you could screw into an electric socket today and it would light. At first, they sold the bulbs and gave away the electricity free. But that didn't last long, and when they started selling electricity it was more expensive than it is now."

One of Edison's early customers was J. P. Morgan, who had his own steam engine generating electricity in his back yard before public electricity was available. "When his first bill came in," according to Dave Gigante of Consolidated Edison, "Morgan began the fine old tradition of complaining about the electric bill. Being J. P.Morgan, he hired his own expert to check it out -- but the expert came back and told him that the bill was correct."

A few years ago, Gigante recalled, Con Ed workers found some of Edison's original wiring under the sidewalks of New York. The two lines of copper, set into a metal pipe and insulated with asphalt, could still carry an electric current.

Those lines were the key to the new age. They connected to the light bulbs, which were the first electric appliances most people had in their homes. And they opened the market for electric irons and toasters, fans and heaters and sewing machines. By the 1890's, such products were advertised everywhere -- at prices that will make visitors to the Smithsonian turn green.