irradiance

noun3

1. •
   The act of irradiating; emission of rays of light.
2. •
   The radiant power received by unit area of surface.

   • The geometry of the cone θ and the irradiance at the image of the carbon block were used to determine the absolute steradiancy of the energy in the cone θ as a radiometer calibration value. — 1959
3. •
   That which irradiates or is irradiated; lustre; splendour; brilliancy.