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 considered light if produced in the U.S. The largest oil field in the world, Saudi Arabia's Ghawar field, produces light crude oils ranging from 33° API (860 kg/m) to 40° API (825 kg/m) In the United States, the price of the front month light sweet crude oil futures contract, traded on the NYMEX commodity exchange (symbol CL), is widely reported as a proxy for the cost of imported crude oil. These contracts have delivery dates in all 12 months of the year. From below $20 a barrel in early 2002, it rose to an intraday peak of $70.85 at the