A man's Christianity should be perfectly visible to all men. You are the light of the world. Think of whether you are a lamp on a stand or under a bushel. I hope you realize this means we need to be different than the darkness. Light, you see, does its work only because it is different than darkness.
Light does nothing in a place that is bright and sunny.
Light has an effect, it makes a difference, only in the darkness. Our light has gone out if we are not separate and different from the world. We need to be sure we properly understand this. Jesus is not saying we are the light source. Jesus is not saying we are the sun or the stars or the lamp.