Definitions for "Longwave Radiation"
The radiation emitted in the spectral wavelength greater than 4 micrometers corresponding to the radiation emitted from the Earth and atmosphere. It is sometimes referred to as terrestrial radiation or infrared radiation, although somewhat imprecisely.
radiation at wavelengths greater than 3 mm, typically originating from sources at terrestrial temperatures (e.g., ground and other terrestrial objects) [W/m2]   langwellige Strahlung (Wärmestrahlung)
Heat emitted by the Earth. It has lower energy and thus a longer wavelength than the incoming sunlight. See shortwave radiation.