Electric light be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap. The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor. Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. Cornish chemist Humphry Davy developed the first incandescent light in 1802, followed
Hartford Electric Light Company for producing heat and steam for their customers. The steam company introduced a new technology in 1881, an electric generator. It was Hartford's first electric service. The Hartford Electric Light Company (HELCO) in 1881 received its charter as an official company and took over the electrical part of Hartford Steam Company. At that time Hartford had about a thousand gaslights in 80 miles of the city streets. It began actual operations of the steam-powered electrical generating plant on Pearl Street in 1882. Austin Cornelius Dunham was the company's first president. The first major project the company did was electrical lighting