Subject: Why do scratches in glass alway seem to form circles around light-sources?

The other day when cleaning up my stuff in our cafeteria I noticed 
something I had seen before and have always wondered about. I looked 
through one of the glass, or thick see-through plastic, pieces of wall 
which seemed to be randomly scratched. With that I mean pretty equally in 
all directions. I noticed that when you look through it in the direction of 
a light-source you always see these scratches in 'circles' around the 
light-source. Why is this, when they are randomly scratched?

Thanks already for the trouble.

Re: Why do scratches in glass alway seem to form circles around light-sources?