Dynamic range

Human eyes have the fantastic ability of being able to handle a vast dynamic range -possibly well over 20 stops.  Thus a stained glass window can appear stunning to the naked eye with a range from almost clear glass to dark vibrant blue.  Sadly even the best cameras will only capture a small segment of this.

Each of the ten segments above is separated by 1/3rd of a stop.  It is clear that the white areas become washed out when overexposed by no more than 2 stops, but the blue areas require at least 3 stops more light in order to become visible.