Interference pattern. Pattern of colours caused by reflections of light through a thin film of oil floating on water. Interference effects arise by reflection in thin films. When the oil film thickness is comparable to the wavelength of light, light waves reflected from the back of the film may be out of phase with light striking the front of the film. This results in interference. When white light hits the oil film, different component colours are either extinguished or reinforced, depending on the light path length through the film. This leads to the sort of pattern seen here.