Because there is little overlap in wavelength between the radiation emitted by the earth and the radiation emitted by the sun, almost all light in the earthÕs atmosphere with a wavelength less than 3 microns is solar in origin, and is
known as solar radiation.  At the same time, almost all light in the earthÕs atmosphere with a wavelength greater than 3 microns comes from the earth or its atmosphere, and is called terrestrial radiation.