One quick suggestion.  Don't use just a spotlight.  Use a general bulb light first, I would suggest a sort of brownish grey color at about 25-30 percent brightness.  Place this one in roughly the same area where your render camera is.  Then add a distance light pointing at the object originating at the point you wish your sunlight or moonlight to come from.  This should be about 70-80% brightness.  Now if you are using a realistic sky for lighting, make sure you insert and properly place a sunlight.  Keep in mind that actual sunlight is not completely white.  It is actually slightly yellow, so set the colors accordingly.  Let me know if this helps.