For a photographer, there is nothing more important than light. Light informs everything a photographer does. A photo, if you will, is a recording of light over a period of time (that period being the shutter-speed the picture was taken at). Every differing detail about that light will change the meaning and emotive content of a photo. Change the lighting and you have a different photo, regardless of whatever is in frame being the same. Definitely a subject likely to be a full blog post later.
But until then, here's the Feature of the Week, courtesy of my good friend Nino Leitner, showing just how much changing the lighting changes the photo.