cinder vs pilot light

cinder

noun
  • Partially or mostly burnt material that results from incomplete combustion of coal or wood etc. 

  • An ember. 

  • Slag from a metal furnace. 

verb
  • To cover with cinders. 

  • To reduce to cinders. 

pilot light

noun
  • A small, persistent flame used to ignite gas. 

  • A small telltale lamp on a dynamo or battery circuit whose brightness indicates the voltage of the current. 

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