bright spot vs side effect

bright spot

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

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

side effect

noun
  • An adverse effect, an unintended consequence of a drug or therapy; usually not a beneficial effect. 

  • A change in state caused by a function call. 

  • An unintended consequence of any action in addition to the intended consequence of that action. 

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