It is a glass ampoule in which there is a metal filament, tungsten or osmium, long and thin that resists the passage of electrical current. The ends of the filament are attached to two contact points located on the metal helmet with a lamp screwed into the socket. A flowing through the filament electric power, the opposition, heated to generate light. Inside the bulb, hermetically isolated from the outside, all air is removed, so the process takes place with inert gases such as nitrogen, neon, argon or krypton.
Power is the amount of work done by the current to travel the filament. It is measured in watts. For example, one speaks of a lamp 60 or 75 watts. The voltage, ie the electrical potential difference in a current through a conductor, measured in volts.
The light bulb was invented in 1879 by the American Thomas Alva Edison (1847-1931). Also developed, telegraph machines, new models of batteries, dynamos and electric motors. He drew worldwide attention in 1877 to develop the phonograph.
The first electric light bulb that Edison built remained on for 40 hours straight.