Because stop lights used to be on the median at the stop line, if you were driving a car like this, with an external sun visor... you wouldn't be able to see when the light changed from stop to go... with this prism gadget placed on the dashboard reflecting the view that the visor blocked, you could look at it and wouldn't have to lean out the side window. It would be the same as holding a mirror at arms length in front of you to see what is reflected from an area above you, instead of bending your neck.
