Pyranometer

A pyranometer (from Greekπῦρ (pyr)'fire' and ἄνω (ano)'above, sky') is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m) from the hemisphere above within a wavelength range 0.3 μm to 3 μm.

A pyranometer with natural output does not require any power to operate as its transducers generates an electrical signal proportional to the solar irradiance. However, recent technical development includes use of electronics in pyranometers, which do require (low) external power.