Incandescent lamps consist of a glass enclosure which contains a low-pressure noble gas and a socket that defines the thread. Inside the lamp is a filament usually made of tungsten wire through which an electrical current is passed. The current heats the filament to an extremely high temperature, typically between 2000K - 6000K. Heated electrons in the tungsten become excited and then transit to lower energy states of the solid and photons, "the light" is released.
The spectrum is typically peaking in the visible light region, but also contains a significant amount of energy in the near infrared wavelengths. Incandescent lamps thus deliver white light at an approximate colour temperature of 2870K.