In the Greek a great deal of emphasis falls on this phrase. He claims to be the Messiah, the Anointed One, the Son of God. Scripture records for us that the Pharisees and the people were incredulous. In him was life, and that life was the light of men. I am the light.
Light means life.
Light signifies life-giving power. Think, for a moment, of the everyday miracle we know as photosynthesis. In photosynthesis light means life. In the presence of light, green plants convert water, carbon dioxide, and minerals into carbohydrates and oxygen. If there would be no light, there would be no photosynthesis.