Alternate Definitions for Irradiance

Irradiance - A radiometric term for the powerof electromagnetic radiation at a surface, per unit area. "Irradiance" isused when the electromagnetic radiation is incident on the surface.Irradiance data may be reported in any units (i.e. counts/s) due to, forexample, being at a particular wavelength, or to being anot-fully-calibrated relative measurement.

In situ measurements of the relative flux or density of
electrically charged particles in the space environment.
May give simple fluxes, but full distribution functions are
sometimes measured.