Source : Webster's Revised Unabridged Dictionary (1913)

Irradiance \Ir*ra"di*ance\, Irradiancy \Ir*ra"di*an*cy\, n.
   [From {Irradiant}.]
   1. The act of irradiating; emission of rays of light.

   2. That which irradiates or is irradiated; luster; splendor;
      irradiation; brilliancy. --Milton.