illumination vs top light

illumination

noun
  • The act of illuminating, or supplying with light; the state of being illuminated. 

  • Adornment of books and manuscripts with colored illustrations. See illuminate (transitive verb). 

  • Festive decoration of houses or buildings with lights. 

  • Enlightening influence; inspiration. 

  • Splendour; brightness. 

top light

noun
  • Light from above; toplighting. 

  • Any glazing above a main window, partition or door 

  • A skylight. 

  • The upper (and usually smaller) part (casement) of a window, often hinged a the top 

How often have the words illumination and top light occurred in a corpus of books? (source: Google Ngram Viewer )