A ball of light, lighting up my pitch dark room..

A few years ago,myself and a friend who was sleeping over,were chatting away in our beds. We had turned off the light and were talking in total darkness.all of the sudden,her face and the rest of my bedroom was totally lit up and we could see each other perfectly.we both jumped up with fright and looked straight out the window,where we saw  something that seemed to be a ball of slightly blue light hovering just outside my window. in distance it would have been near the middle of my garden and in height,just above the roof of the house.we froze as we looked at it and after about a good five to six seconds,it shot off extremely fast.we then were left in a darkend room again. Neither of us have any idea of what it could have been and we regularly wonder about it.My dad suggested it could have been a fireball,but it was totaly soundless. it's not like there's many people you can tell this kind of thing to,so i dont really bother(even though i want to tell everyone)but i would love to hear from somebody who could tell me what it could have been. the curiosity hasn't faded in the last few years and i don't think it ever will.
No date provided by witness.  We have assigned an arbitrary date, such that the case will sort to the time period of "a few years ago," but it is pure speculation.  PD