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
Philosophical Transactions of the Royal Society A engineering sciences, edited by leading authorities and comprising original research, reviews and opinions from prominent researchers. Past issue titles include "Supercritical fluids - green solvents for green chemistry?", "Tsunamis: Bridging science, engineering and society", "Spatial transformations: from fundamentals to applications", and "Before, behind and beyond the discovery of the Higgs boson". "Philosophical Transactions of the Royal Society" was established in 1665 by the Royal Society and is the oldest scientific journal in the English-speaking world. Henry Oldenburg was appointed as the first (joint) secretary to the society and he was also the first editor of the society's journal. In 1887