I have heard people say that we are like the moon and God is like the sun in that He gives off light and we reflect that light. We are not light in ourselves, we just reflect Him.
For argument's sake, though, let me take this analogy to task. What does the moon do to reflect the light of the sun? Nothing! It just floats in space while the sun does all the burning.
Too many Christians have taken on this aspect of this particular analogy. They let God do all the work and assume that somehow His light will just shine through us.
"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." - Matthew 5:14-16 (NIV)
I know that for some this seems to contradict not letting your right hand know what your left hand is doing (Matt. 6:3), but that command was specifically about giving to the needy.
This command is more about how you live. Intentionally doing things that will bring honor to God, and show the world what matters to Him. You don't accidentally do these things. You have to look for ways to do this; pray for opportunities, then make the most of them.
What has your faith caused you to do that rips you out of your comfort zone and ignites the light you are to be in this dark world? What have you done to intentionally bring glory to God? How have you "loved your neighbor as you love yourself" in action?