July 14th The Best Thing Since Sliced Bread

I am not sure how many other car park facilities have these. Lights up top so not only is there a lit up sign telling you how many empty spaces are down an aisle, but also these lights up top that indicate green for empty spaces and red for taken. Although  I have seen the odd purple one pop up and have no idea what that signifies. If anyone could enlighten me that would be appreciated.