Incandescent lamp

Definition
An incandescent lamp is an artificial light source in which light is emitted by an incandescent body heated by an electric current to a high temperature. As the incandescent body, a spiral made of a refractory metal (most often — tungsten) or a carbon thread is most often used. To avoid oxidation of the glow body in contact with air, it is placed in a vacuum flask, or a flask filled with inert gases or vapors.

Operating principle
In an incandescent lamp, the effect of heating the incandescent body when an electric current flows through it (the thermal effect of the current) is used. The temperature of the incandescent body increases after the electrical circuit is closed. All bodies whose temperature exceeds the temperature of absolute zero emit electromagnetic thermal radiation in accordance with Planck's law. The spectral density of the radiation power (Planck function) has a maximum, the wavelength of which depends on the temperature on the wavelength scale. The position of the maximum in the radiation spectrum shifts with increasing temperature towards smaller wavelengths (Wien's law of displacement). To obtain visible radiation, it is necessary that the temperature of the emitting body exceeds 570 °C (the temperature of the beginning of the red glow visible to the human eye in the dark). For human vision, the optimal, physiologically most convenient spectral composition of visible light corresponds to the radiation of a completely black body with a surface temperature of the Sun's photosphere of 5770 K. However, there are no known solid substances that can withstand the temperature of the Sun's photosphere without destruction, so the operating temperatures of the filaments of incandescent lamps lie in the range of 2000-2800 °C.

Varieties
Incandescent lamps are divided into (arranged in order of increasing efficiency):
Vacuum (the simplest)
Argon (nitrogen-argon)
KryptoniteXenon-halogen with an IR reflector (since most of the lamp's radiation falls on the IR range, the reflection of IR radiation inside the lamp significantly increases the efficiency, produced for hunting lanterns)
Incandescent lamps with a coating that converts IR radiation into the visible range. The development of lamps with a high-temperature phosphor, which emits the visible spectrum when heated, is underway.

The structure of a modern lamp
The design of a modern incandescent lamp. In the diagram: 1-flask; 2-flask cavity (evacuated or filled with gas); 3-glow body; 4, 5-electrodes (current inputs); 6-hooks - holders of the glow body; 7-lamp leg; 8-external link of the current lead, fuse; 9-cap body; 10-cap insulator (glass); 11-contact of the bottom of the cap.