Open the Window

You have a garage and it has only one window. The window is one foot high, one foot wide and square. You want to let more light in but you cannot add any more windows, so you deside to modify the one you have. When finished, the window is one foot high, one foot wide and square but it lets twice as much light in. How?

 

As usual: no cutting down trees, moving the garage, changing the curtains or stuff like that.