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
Royal Society of Sciences in Uppsala Royal Society of Sciences in Uppsala The Royal Society of Sciences in Uppsala (Swedish "Kungliga Vetenskaps-Societeten i Uppsala"), is the oldest of the royal academies in Sweden. The society has, by royal decree of 1906, 50 Swedish fellows and 100 foreign. Early members included Emanuel Swedenborg and Anders Celsius. The Royal Swedish Academy of Sciences was founded in Stockholm 1739, and its founders (some of which were members in Uppsala) specifically wanted an academy which was different from the Uppsala academy. The Academy was founded 1710 in Uppsala on the initiative of the university librarian Erik Benzelius (jr) (later archbishop)