Wiktionary
pyranometer
n. An actinometer used to measure solar radiation incident on a surface; a solarimeter
Wikipedia
Pyranometer
A pyranometer 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. The name pyranometer stems from the Greek words πῦρ (pyr), meaning "fire", and ἄνω (ano), meaning "above, sky".
A typical pyranometer does not require any power to operate.''