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
Royal Society of Thailand is on a par with weapon" (ปัญญาประดุจดังอาวุธ). The light of the sword represents the light of wisdom. The crown represents the monarch. Perhaps the most well-known work of the society is the prescriptive "Royal Institute Dictionary" (พจนานุกรม ฉบับราชบัณฑิตยสถาน, in English often abbreviated RID). The society has published four fully revised editions of the dictionary, and many intermittent reprintings with minor revisions. Each of the major revisions is associated with a significant year in Thai history, although in the case of the 1999 and 2011 editions, the actual publication date is a later year. The Royal Society publishes guidelines for spelling