The 13th of December is Lucia day and a special day in Sweden.
I've searched on YouTube and found a few videos that give a image about this tradition.
The story about this tradition is long and mysterious. It is however not a Christian tradition strictly speeking. Lucia was a saint, but the tradition to sing on this day comes from farm-hands's and students's tradition to walk from farm to farm on St Staffan's day to sing and beg for money and/or booze. The character of a woman dressed in white comes from Germany where St Nicolaus gave presents to Catholic children. The Protestants then dressed up a woman as Jesus (a boy could not be that innosent and pure) and she gave presents to Protestant children.
Music that inspired me