A simpler setup would be to have two flat pieces of glass in contact along one edge and a narrow angle between their two faces. If the separation between the top surface of the first piece of glass and the top surface of the second piece of glass is, at some point, such that light beams reflected from each are synchronized or in phase, then the reflected light will be bright, but if the two beams are half a cycle out of phase, then at that point the two beams will cancel each other and what reflected light there is will not be bright.