bright spot vs strength

bright spot

noun
  • A good part of something that is otherwise fairly bad or unpleasant. 

  • Used other than figuratively or idiomatically: see bright, spot. 

strength

noun
  • A positive attribute. 

  • The intensity of a force or power; potency. 

  • The quality or degree of being strong. 

  • The strongest part of something; that on which confidence or reliance is based. 

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