What does Jesus means when He says, "You are the light of the world"?

In Matthew 5:14 Jesus, when talking to his disciples, says: "You are the light of the world. A city on a hill cannot be hidden. Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. In the same way, let your light shine before men, that they may see your good deeds and praise your Father in heaven." In other words, if you know something to be true and right, it is natural to demonstrate that you know it and allow the conviction of your belief to illuminate whatever is around you. He is asking his disciples to shine brightly in what they do and say and to live their lives in such a way that everyone will see that the way of Christ is valid and works for good in life.