Source : Webster's Revised Unabridged Dictionary (1913)

Phototherapy \Pho`to*ther"a*py\, n. (Med.)
   The application of light for therapeutic purposes, esp. for
   treating diseases of the skin. -- {Pho`to*the*rap"ic},
   {Pho`to*ther`a*peu"tic}, a.

Source : WordNet®

phototherapy
     n : the use of strong light to treat acne or hyperbilirubinemia
         of the newborn