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 Canada at than the US at , resulting in slightly different density values. A wide variety of benchmark crude oils worldwide are considered to be light. The most prominent in North America is West Texas Intermediate which has an API gravity of 39.6° API (827 kg/m). It is often referred to by publications when quoting oil prices. The most commonly referenced benchmark oil from Europe is Brent Crude, which is 38.06° API (835 kg/m). The third most commonly quoted benchmark is Dubai Crude, which is 31° API (871 kg/m). This is considered light by Arabian standards but would not be