You Are the Light (Matthew 5:14-16)

Our Lord says that you are the light of the world. This almost implies that we are call attention to our good works and the good things that we do.  This would mean that Christ is commanding us to be self righteous and to engage in a piety competition.  Are we really supposed to parade around our good works?  Why would Christ warn us about the outward pious acts of the pharisees?  How does being the light of the world humble us and exalt our God?