Because the figure lying down gives the impression of being the effigy of a knight in a tomb, I've always thought that the window would be a reflection of that... near several actual tombs that I've seen in old medieval churches, the windows carry symbolic messages of hope- often of the resurrection.
So that's probably why I interpret that window in the card the way that I do- I see it as being Christ risen in the Garden of Gethsemane, with Mary Magdelene kneeling on the right, (that might possibly be the tomb in the background, with the light illuminating the doorway)... I saw this as implying that although there might be a time of difficulty ahead which could lead to either physical, mental, or even spiritual exhaustion- there will be light at the end of the tunnel, so to speak. To allow the body, mind, and spirit a place in which to heal and recover.
elnor