The resistivity of tungsten wire is 5.3*10^-8, the melting point of tungsten is high, the resistivity is high, the intensity is good, and the steam is low. It is the best material to make the incandescent filament in all pure metals. However, because of the great hardness and brittleness of tungsten, it is difficult to process. When the electric current is heated to a certain temperature through the tungsten wire, the resistance value of the tungsten wire is increased to a certain value (The resistance value of general wire increases with the increase of temperature). At room temperature, this resistance should be 1370 -2000 degrees, but when the length of wire cross-sectional area changed, the resistance value will not change. In 1909, Coolidge invented the processing technology of tungsten filament, which played a decisive role in the production and promotion of incandescent bulbs. Its basic principle has been used today.