@see http://www.edesign.nl/examples/sunlightmap/index.php
@see http://www.edesign.nl/examples/sunlightmap/map.php?show_source
@see http://www.edesign.nl/examples/sunlightmap/sphere.class.php?show_source
@see http://www.edesign.nl/examples/sunlightmap/vec3.class.php?show_source
@see http://www.edesign.nl/2009/05/14/math-behind-a-world-sunlight-map/comment-page-1