John 8:12

Again Jesus spoke to [the Scribes and the Pharisees], saying, I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life."

There is really little more to be said, so what follows can be seen as trivia, and skipped:

The setting is important here. Jesus is saying this in the Temple, in Jerusalem, during the Festival of Booths. During that Festival, huge golden lamps were lit in the Temple court, giving great light to the entrance to Israel's chief place of worship. Jesus is saying, in essence, "You think these give light; you've not seen anything yet."

The great and glorious lamps lit only the Temple court. Jesus is the light of the world, and those who follow Jesus will never walk in darkness.