There is no definite article in front of “light” as there is in John 8:12 so this could read “While I am in the world, I am light to the world.” The darkness would soon come when Jesus was no longer in the world and yet, that darkness would no longer be as total as it was in the past because there would be many “lights” to enlighten the night. Who are those lights? His followers — you and me!

Matthew 5:14  “You are the light of the world. A city on a hill cannot be hidden.

He has made us to be “lights” so we can shine. Are you?

Philippians 2:15  so that you may become blameless and pure, children of God without fault in a crooked and depraved generation, in which you shine like stars in the universe

Jesus has just shown Himself to be light in the moral sense by shining on the actions and motives of the religious leaders of the Jews and He is now going to show Himself to be light in a physical and a spiritual sense by healing the man born blind and enabling him to see the light he has never been able to see with his eyes and also with his heart.