Interference pattern. Light micrograph of interference patterns on a soap film. The different colours are due to interference of reflected light waves. Some incidental light reflects off the surface of the film, while the rest of the light travels through to the back of the film and is reflected. The thickness of the film varies across its surface, causing certain wavelengths to be extinguished, producing a variation in colour. Magnification: x25 when printed at 10 centimetres wide.