I think this song is about how messed up and dark the world is and if you see that then you should be the one to set an example for others and brighten it up a bit. "When the sun goes down and the lights burn out" when the world is at its worst and you think there's no hope for humanity "then it's time for you to shine" then you should be the hope for humanity and be the change you wish to see in the world. I think its a really helpful thing to visualize ourselves as lights in the darkness. While everyone else is complaining and badmouthing others, say something happy or give them a compliment. And with songs like this you know that you're not alone, that there are other people making the effort too.