The incandescent lamp was invented by the American Thomas Alva Edison, 1847 to 1931. It consists of an airless vacuum bulb in which there is a metallic filament that is made to glow, hence the name incandescent lamp. The basic principle invented by Edison has survived to the present day, except for the tungsten filament, which replaces the carbon filament of the time, and in addition, the glass bulb may be filled with an inactive inert gas, such as krypton.
The tungsten filament is extremely thin, about 0.05 mm, coiled, and can withstand high temperatures. It can be manufactured very precisely and does not burn out in the glass bulb filled with inert gas because there is no oxygen in this bulb. Light emission is achieved by heating the filament; it has high red components and, depending on the wattage, color temperatures range from 1,500 Kelvin (K) for a 40 W lamp to 2,800 K for a 100 W lamp.
Luminous efficacy is very poor and only reaches values of a maximum of 20 lumens per watt( lm/W), which corresponds to a percentage luminous efficacy of 20%. The rest is heat loss. The temperature of the filament can be derived from the color temperature; this is between 1,200 °C and 2,500 °C. The service life of incandescent lamps is over a thousand hours, which is a fraction of the service life of power LEDs.
Incandescent lamps are available for low and all line voltages, and they can operate on DC and AC voltages. They have standardized lamp bases, either threaded bases such as E27 or E14, which are screwed into the lamp socket, or plug-in bases such as 2G10 or G23. In the case of threaded bases, the thread forms the base contact, and a foot contact on the underside of the base forms the second contact for the circuit.