Another example of interference that is often observed is interference from a thin film. Light incident on the surface of a thin film is reflected from the surface and transmitted through the surface. The transmitted light is then reflected from the interface between the thin film and the underlying substrate. The distance that the light travels through the thin film and back to the initial interface will cause a phase shift. When the transmitted wave returns to the original medium it will interfere with light that is reflected off of the surface of the thin film. The interference will depend on the amount of phase shift introduced due to the increased path length. ( = constructive, = /2 destructive) If constructive interference occurs the light intensity of that particular color is enhanced. If destructive interference occurs the intensity of a particular color is diminished. When we use white light certain colors will be eliminated at certain incident angles. The result is color pattern that changes with the position of the observer.