Why Pumkins on Halloween?

It is common practice around Halloween to hollow out a pumpkin, carve a face on it and light the inside with a candle.  But why is this related to Halloween? These creations are usually called jack-o-lanterns and there is a very extensive story behind the tradition.

The "jack" in jack-o-lantern refers to Stingy Jack.  The story goes that he was a somewhat of a bum, always drunk, who liked to play trick on people.  The devil heard of him and wanted to meet him, and see if he lived up to the rumors about him.  One day Jack crossed paths with the devil in a bar.  He trades his soul for the cost of his drinks.  When the devil transformed himself into a coin to pay for the drinks, Jack put the coin in his pocket.  Also in his pocket was a cross preventing the devil from transforming back into himself.  Jack lets the devil out and makes another deal with him for another ten years of life.  Ten years later when the devil comes back for him, Jack had another request.  He asked the devil to climb a nearby tree and get him an apple.  He then put crosses all around the base of the tree, and again trapped the devil.  In exchange for his freedom, the devil said he would not take Jack's soul.  When Jack finally died he was not allowed into heaven for all of the bad things he had done during his life.  He went to the gates of Hell, but the devil honoring his agreement would not take Jack's soul.  Jack asked for one final request, some light to travel back to earth with.  The devil knowing he had won gave Jack an ember from the fires of Hell.  Jack carried the ember in a hollowed out turnip, one of his favorite foods from when he was living.  It is said that he roams the earth with his ember.

The tradition began in Ireland where they would hollow out turnips calling them "Jack of the Lantern".  They started to carve faces into them and placing them near doors and windows to ward off Jack or other evil spirits.  When they immigrated to the United States, the medium changed to pumpkins.  Today it is common to carve out jack-o-lanterns around Halloween.