Circular wave interference, illustration. Patterns are formed by the interference of two circular waves interacting with each other. The waves are produced by point sources. At the point where a wave peak from one hits a wave peak from another, or a trough hits a trough, they reinforce each other. This is known as constructive interference, and is shown by areas of light and dark shade. Areas of destructive interference are where a trough hits a peak or vice versa and they cancel each other out.