illumination vs opacity

illumination

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

  • Festive decoration of houses or buildings with lights. 

  • Enlightening influence; inspiration. 

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

  • Splendour; brightness. 

opacity

noun
  • The state or quality of being opaque, not allowing light to pass through 

  • The state or quality of being inaccessible to understanding. 

  • A measure of relative impenetrability to electromagnetic radiation such as light. 

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