http://www.geocities.com/thescience...ffraction.html] Refer to this web site, please. The brightness of the colour is proportional to its amplitude? I can understand why the middle of the screen is the brightest, but in my mind, I think there should be only one area which is bright for a single-slit. Is that light has many beams and able to create interference for even only a single-slit? The diffraction of a light beam is really different from that of a water wave, isn't it?