The Collaborative International Dictionary of English v.0.48:

Radiance \Ra"di*ance\ (r[=a]"d[i^]*ans), Radiancy \Ra"di*an*cy\
   (r[=a]"d[i^]*an*s[y^]), n.
   The quality of being radiant; brilliancy; effulgence; vivid
   brightness; as, the radiance of the sun.
   [1913 Webster]

         Girt with omnipotence, with radiance crowned. --Milton.
   [1913 Webster]

         What radiancy of glory,
         What light beyond compare !              --Neale.
   [1913 Webster]

   Syn: Luster; brilliancy; splendor; glare; glitter.
        [1913 Webster]

WordNet (r) 3.0 (2006):

radiancy
    n 1: the quality of being bright and sending out rays of light
         [syn: radiance, radiancy, shine, effulgence,
         refulgence, refulgency]