Set light to something
Definition 1 of 1
Pro Tip 1/3Literal Use
Used to describe actually starting a fire, often for a purpose like burning leaves or trash. 
In autumn, the farmer set light to the stubble in his fields.
Pro Tip 2/3Metaphorical Use
Sometimes used metaphorically to imply causing excitement or starting something energetically. 
Her speech set light to the audience's passion.
Pro Tip 3/3Non-literal Warning
Not to be confused with 'shed light on', which means to clarify or explain something. 
Incorrect: He set light to the mystery. Correct: He shed light on the mystery.