Oil film interference on water.

Oil-film interference on water. Constructive and destructive interference of reflected light waves causes the colorful patterns we sometimes observe in thin films, such as layers of oil on water, and also soap bubbles. Constructive interference results in a color appearing brightly, and destructive interference results in a dimming or absence of that color. In this demo, white light from a reading lamp shines down upon a white-paper diffuser-screen. The light from the screen illuminates a dark plastic lid filled with water. A glass rod coated with oil barely touches the water causing a thin oil film on the surface of the water. The white light is partially reflected from the air-to-oil and oil-to-water interfaces, and the constructive and destructive interference of various wavelengths creates multi-colored patterns. A video camera and video projector put the colored fringes on a large screen.