The Collaborative International Dictionary of English v.0.48:

irradiant \ir*ra"di*ant\ ([i^]r*r[=a]"d[i^]*ant), a. [L.
   irradians, -antis, p. pr. See Irradiate.]
   Irradiating or illuminating; as, the irradiant moon. --Boyse.
   [1913 Webster]