At any given instant, each photoreceptor in my eye is receiving a multitude of light waves at many frequencies and all out of phase. In other words at any instant, a photoreceptor is getting troughs and peaks and everything in between. The sum of all these waves is zero.*These light waves are all out of phase since they are randomly generated by multiple different tungsten atoms from all over the filament in the light. But Throwing thousands of pebbles into a pond still generates waves on the shore - they don't cancel out. Why not?