bedtime vs blackness

bedtime

noun
  • The time or hour at which one retires to bed in order to sleep. 

blackness

noun
  • The state of being of African descent. 

  • The quality of being evil or dismal. 

  • The state or quality of being black in colour. 

  • The experiences and culture of African-American people. 

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