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
Atmospheric distillation of crude oil Atmospheric distillation of crude oil Distillation of crude oil is typically performed either under atmospheric pressure and under a vacuum. Low boiling fractions usually vaporize below 400 °C at atmospheric pressure without cracking the hydrocarbon compounds. Therefore, all the low boiling fractions of crude oil are separated by atmospheric distillation. A crude distillation unit (CDU) consists of pre-flash distillation column. The petroleum products obtained from the distillation process are light, medium, and heavy naphtha, kerosene, diesel, and oil residue. Crude oil obtained from the desalter at temperature of 250 °C–260 °C is further heated by a tube-still heater to a