If I understand your question correctly, you are asking about crepuscular rays. You'll find an excellent picture (and explanation) here:
http://epod.typepad.com/b...epuscular-rays.html.
In the photo, you see that there are alternating light and dark stripes. The light regions come from sunlight shining on dust or other types of aerosols (tiny particles suspended in the air). The dark stripes are mostly from shadows of clouds. The main factor influencing the angle of the rays (whether they shine up or down) is where the Sun is in the sky and where the clouds are. However, the sun's rays will always appear to converge back to the Sun, even though they are all parallel, in the same way that railroad tracks appear to converge to a point (perspective effect).
The photo is copyrighted by David K. Lynch, Thule Scientific, http://www.thulescientific.com.