Darkness made the light stunning. Candles along the pathways, strings of colored lights wound round evergreen trees, and spotlights aimed at carolers, illuminated the Christmas Walk at the Dow Gardens this weekend. There really wasn't that much light, just strategically placed candles and twinkling strings of tiny lights along the paths. But the thousands of visitors who toured the gardens will not remember the darkness, great as it was. They will remember the light.