Blinds Effect

I was just watching a movie at my friend's apartment and noticed that her light on the front porch caused a cool shadow on the wall through the blinds in her front window. I didn't have a lot of time to analyze exactly what was causing the effect because we were watching a movie. However it was quite interesting, the shape was almost a semi-circle of individual lines of light. As best I could tell it was the angle that the light was coming in combined with the placement of the blinds in relation to the wall that caused the shadows to be cast and the light to be let through in the way that they were.