Irradiation illusion The white square against a black background on the left appears to be larger than the black square against a white background on the right They are actually the same size This is a demonstration of the irradiation effect The fluid inside our eyes is not completely clear consequently it will scatter light travelling to the retina light detector at the rear of the eye So brighter areas which reflect more light will spill over and encroach upon darker areas of the retinal image Thus a light area will appear slightly larger than it actually is