The pyrgeometer LP PIRG 01 is used to measure the far infrared radiation (FIR). Its use is mainly in the meteorological fi eld. Measures are referred to radiations with wavelength greater than 4.5 μm . The far infrared radiation derives from the measure of the thermopile output signal and from the knowledge of the instrument temperature. The temperature measure is performed by a 10kΩ NTC which is inside the body of the pyrgeometer. The pyrgeometer can be used also for the study of energy balance. In this case, besides another pyrgeometer which measures infrared radiation upwards, it is necessary to have an albedometer (LP PYRA 05 or LP PYRA 06) to measure short wavelengths radiation (<3μm) .