The Pharisees are the truly blind ones in this story. Their rigid understanding of God made them spiritually blind. Their commitment to their own system of works meant that only the people who kept the legalistic requirements of the laws could be considered righteous, and thus their hearts were closed to the movement of God's Spirit.
The key attribute of light is that it allows us to see things as they really are. John's gospel from the very beginning presents the world as a place filled with darkness. This darkness is spiritual confusion caused by sin, and for the most part we are powerless to deal with it and find our way on our own.
It is important to understand the nature of the light that Jesus is for us; this light is not just about knowledge, knowing and believing the right things about God and ourselves. The light actually leads us into God's presence. By receiving Jesus, we enter into a true relationship with God.
Jesus wants to heal our spiritual blindness so that we can see God for who he really is, as the Creator who loves us and wants to be in relationship with us forever; and to see ourselves for who we really are, the beloved of God whom Jesus came into the world to seek and to save.