The Collaborative International Dictionary of English v.0.48:

Insolation \In`so*la"tion\, n. [L. insolatio: cf. F.
   insolation.]
   [1913 Webster]
   1. The act or process to exposing to the rays of the sun for
      the purpose of drying or maturing, as fruits, drugs, etc.,
      or of rendering acid, as vinegar.
      [1913 Webster]

   2. (Med.)
      (a) A sunstroke.
      (b) Exposure of a patient to the sun's rays; a sun bath.
          [1913 Webster]

   3. (Meteorology) The amount of sunlight impinging on the
      Earth's surface.
      [PJC]

WordNet (r) 3.0 (2006):

insolation
    n 1: sudden prostration due to exposure to the sun or excessive
         heat [syn: sunstroke, insolation, thermic fever,
         siriasis]
    2: incident solar radiation
    3: therapeutic exposure to sunlight [syn: heliotherapy,
       insolation]