safety lamp, oil lamp designed for safe use in mines and other places where flammable gases such as firedamp (see damp) may be present. Its invention (c.1816) is usually attributed to Sir Humphry Davy. The Davy lamp is based upon the principle that to be ignited a substance must first be heated to its kindling temperature and that if such heating is prevented combustion will not occur. The flame in the lamp is surrounded by a metal-gauze screen that distributes the heat over a large area so that the maximum temperature of the screen is below the ignition temperature of the flammable gas mixture (e.g., firedamp). Improvements devised by K. G. Bischof and others include special locks to prevent the accidental opening of the lamp and devices to permit the lamp to be held upside down without danger. If firedamp or related gas mixtures are present in a mine, the Davy lamp flame burns higher and with a blue halo; the height of the flame and color of the halo indicate the amount of combustible gas in the air. If the mine air is deficient in oxygen, the lamp flame is extinguished. Coal miners often placed the safety lamp close to the ground to detect gases, e.g., carbon dioxide, that are denser than air and thus collect in poorly ventilated depressions in the mine. Other gas-detecting devices are now more commonly used, e.g., the methanometer; as a light source the Davy lamp has been replaced by electric lighting.

lamp shell, common name for animals of the phylum Brachiopoda.

lamp, originally a vessel for holding oil or some combustible substance that could be burned through a wick for illumination; the term has been extended to other lighting devices. Stones, shells, and other objects of suitable shape were used for burning oil in the Paleolithic period. In Egypt and the Middle East saucerlike terra-cotta lamps were early known. In Greece torches were supplemented in the 6th cent. B.C. with pottery and metal lamps. The Greeks often used a cylindrical spout for the wick. The Romans used a superior closed type of lamp, often with multiple spouts. The float-wick lamp, in which the wick is supported above the oil, was probably of Egyptian origin; it survived in the West chiefly as a sanctuary lamp. The seven-branched candlestick of the Hebrews is believed to have been a support for a group of float-wick lamps. Its symbolical descendant is the eight-branched Hanukkah lamp, usually of the spouted saucer type. There was little improvement in the design of lamps from ancient times to the 18th cent. The Betty lamp of the North American colonists and pioneers was a spouted saucer lamp with a lid. Lamps were smoky because the center of the round wick received too little air for complete combustion. Flat wicks, introduced late in the 18th cent., made less smoke, but the light was somewhat dim. At about the same time a circular wick with an open center was invented by Aimé Argand, a Swiss chemist, who also introduced the glass lamp chimney. One- and two-burner lamps were common from the late 18th cent., and these often burned whale oil. Kerosene, used from the mid-19th cent., almost entirely superseded other oils for lamps; the kerosene lamp is still used for lighting where gas and electricity (the most common form of energy for lamps in industrialized countries) are not available and in many safety, signal, and hurricane lamps. In literature and art the lamp has often symbolized learning or knowledge; in religious ritual, honor to the divine. For the development of the electric lamp, see lighting.

Any of various devices that produce light by heating a suitable material to a high temperature. In an electric incandescent lamp, or lightbulb, a filament is enclosed in a glass shell that is either evacuated or filled with an inert gas. The filament gives off light when heated by an electric current. The first practical electric incandescent lamps were independently produced in the late 1870s by Joseph Swan and Thomas Alva Edison. Edison has received the major credit because of his development of the power lines and other equipment needed for a lighting system. Inefficient in comparison with fluorescent lamps and electric discharge lamps, incandescent lighting is today reserved mainly for domestic use. Seealso halogen lamp.

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or vapor lamp

Lighting device consisting of a transparent container within which a gas is energized by an applied voltage and made to glow. After practical generators were devised in the 19th century, many experimenters applied electric power to tubes of gas. From circa 1900, electric discharge lamps were in use in Europe and the U.S. Fluorescent, neon, mercury, sodium, and metal-halide lamps are of the electric discharge variety.

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Type of electric discharge lamp consisting of a glass tube filled with a mixture of argon and mercury vapor. A current of electricity causes the vapor to produce ultraviolet radiation that, in turn, excites a phosphor coating on the inside of the tube, causing it to fluoresce, or reradiate the energy as visible light. Fluorescent lamps are cooler and more efficient than incandescent lamps. They are commonly installed with diffusers as part of a suspended ceiling system. Seealso fluorescence.

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