A clear and fun object lesson to show what it means to let our light shine.
In this object lesson we see that we need the power and filling of the Holy Spirit to truly be that light. You could also combine this object lesson with the parable of the wise and foolish virgins.
You can use this idea also as a children's moment in your church service. 
Themes:
Being the light of the world, being filled with the Holy Spirit, letting your light shine
Bible refence:
“You are the light of the world. A town built 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 others, that they may see your good deeds and glorify your Father in heaven." (Matthew 5: 14-16)