Quote Originally Posted by tkamiya View Post

The only rationale I can come up with is that the point source light falls on the subject. In this journey of the light, it spreads as it travels. Once the subject is illuminated, the reflected light doesn't spread. I don't know why and can't explain why.
You will not have to search for an explanation why it would not spread, because it indeed does spread.
Read the thread. All is revealed. Several times, in fact.