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
Light crude oil less than 850 kg/m (API gravity greater than 35° API) The Mexican state oil company, Pemex, defines light crude oil as being between 27° API (893 kg/m) and 38° API (835 kg/m). This variation in definition occurred because countries such as Canada and Mexico tend to have heavier crude oils than are commonly found in the United States, whose large oil fields historically produced lighter oils than are found in many other countries. Canada also uses the SI of units to measure oil rather than American oil industry conventional units, and the base temperature for density calculations is different in