What is light and what is dark? light *noun* 1. the natural agent that stimulates sight and makes things visible "the light of the sun" 2. an expression in someone's eyes indicating a particular emotion or mood "there was a light in his eyes" dark *noun* 1. the absence of light in a place ”he was sat in the dark” 2. a dark colour or shade ”lights and darks should be washed separately” *Oxford dictionary