An Etymological Dictionary of Astronomy and Astrophysics

The → energy at all → wavelengths that is incident on unit area of surface in unit time. It is measured in Watts per square meter.

Etymology (EN): Irradiance, from ir- variant of → in- (by assimilation) before r + radi(ant), → radiation, + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.

Etymology (PE): Tâbešdâri, from tâbeš, → radiation, + dâri, verbal noun from dâštan “to have, hold,” → property.