Bulb as in electric light bulb is not the technical term to describe a device which is specifically designed to emit light. The correct term is lamp. Light emitting devices - lamps fall into 2 x basic categories: incandescent lamps and discharge lamps. The former employs the heating effect of an electric current. A filament usually made from nichrome deliberately offers a resistance to the flow of current converting electrical energy into heat energy. The heat developed in a typical incandescent - filament - reaches operatring temperatures in the order of 3000 C. At this temeperature the filament glows white and incandesces - emits light - hence the term incandescent lamp. In order to prevent the filament from burning it is placed in a glass envelope which contains either an inert gas or a vacuum. The shape of the glass envelope h resembles the shape of a horticultural bulb .... as in tulip, dafodil etc
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