Most infrared sources are thermal sources based on the black body model. A black body is an object which emits electromagnetic radiation as a function of its temperature T. The radiated power is propotional to T⁴, while the emission wavelength range is proportional to 1/T.

The globar source (SiC) used in mid-infrared instruments is a filament carrying an electric current. The current induces thermal heating of the filament (about 2,000 K), resulting in light emission.