Most photo classes start with: Photography means painting with light. 

But when most people take a photo or look at a photo, that is not what they see. They see the subject. 'The light' is usually invisible to them.

A big part of learning photography is learning to see light. It's this is not meant literally. That said, one day, a few years back, I noticed a slice of light coming into our house. I grabbed my camera and took a picture. Since that day I have kept my eye out for the moments when the light calls out and shouts “Here I am!”