Have some fun with your gullible friends and make them think your phone comes with a built-in Solar Panel that allows you to charge your phone.
It uses the intensity from the front-facing camera to detect how much "sunlight" there is and shows the charge amount. Put your hand over the solar panel (and our little secret: the camera or light sensor as well) and let your friends be awed by the drop in charging power.
Note: This app doesn't actually charge your phone!
Now uses the Phone's Light Sensor for a much improved experience! Only shows charging when charge level is big enough.
Added authentic charge sound and live tile.
This is where messing with your friends began.