Operation of incandescent lamp
The principle of the carbon filament lamp is that light arises due to heating an incandescent filament in the light source. As more power is fed to the filament, its temperature will increase and when the temperature is high enough, the filament will start to glow. The higher the power, the hotter (thousands of degrees Centigrade) the filament will be, and the whiter the light that is emitted. So, incandescent lamps operate in such way that the temperature is decisive for the colour temperature. A slightly lower temperature is a less heavy loading of the lamp, which is the reason why dimmed incandescent lamps often have a longer lifetime. Relatively speaking, the operation of an incandescent lamp is not very economical, but highly atmospheric.
How does the filament start glowing?
The spiral-shaped filament is made of tungsten, because this material has both a high melting point and a high specific resistance to electric current. When in direct contact with the air, the filament will immediately burn due to the reaction with oxygen. For that reason, glass is used to form a protective atmosphere around the filament, which is vacuum-pumped or filled with a rare gas such as argon.
The operation of incandescent lamps is a vulnerable process. The filament of a burning lamp is highly fragile, which is why it is supported internally by carriers. An increased number of carriers makes for a lamp better suited for heavy-duty operations such as an application for hand inspection lamps.