The Collaborative International Dictionary of English v.0.48:

Irradiate \Ir*ra"di*ate\ ([i^]r*r[=a]"d[i^]*[=a]t), v. t. [imp.
   & p. p. Irradiated ([i^]r*r[=a]"d[i^]*[=a]`t[e^]d); p. pr.
   & vb. n. Irradiating ([i^]r*r[=a]"d[i^]*[=a]`t[i^]ng).] [L.
   irradiatus, p. p. of irradiate. See In- in, and Radiate.]
   [1913 Webster]
   1. To throw rays of light upon; to illuminate; to brighten;
      to adorn with luster.
      [1913 Webster]

            Thy smile irradiates yon blue fields. --Sir W.
                                                  Jones.
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   2. To enlighten intellectually; to illuminate; as, to
      irradiate the mind. --Bp. Bull.
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   3. To animate by heat or light. --Sir M. Hale.
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   4. To radiate, shed, or diffuse.
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            A splendid fa[,c]ade, . . . irradiating hospitality.
                                                  --H. James.
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   5. To expose to radiation of any kind, especially ionizing
      radiation; as, to sterilize food by irradiating it with
      gamma rays; one can cause mutations in bacteria by
      irradiating them with ultraviolet light.
      [PJC]