I'm really confused about the way the light can suffer interference. I'll try to explain the way I think all this occurs and the question I have if this explanation was correct. I would like you guys to correct me if anything I say is wrong and to try to explain me the final question. Light is a set of photons that oscilates creating an eletric and a magnetic field around them. When 2 photons are too close their eletric/magnetic fields can interact generating the interference. But this would need the 2 photons to be really close, doesn't? And this interference would occur only while the 2 photons were together. Like in the picture. http://img13.imageshack.us/img13/5903/20573870.png [Broken] Now look at the picture http://img89.imageshack.us/img89/1899/skhgfshgdfgsdg.png [Broken] Consider all light rays to be almost perpendicular to the surface. So the difference of luminous path would be 2d and, like all interference book says: If 2d = (2n+1)/2 λ - constructive interference If 2d = n λ - destructive interference This is due to the phase inversion in B. OK, BUT WHERE THE HELL DOES THE INTERFERENCE OCCURS? B isn't in the same place than D, so the interference can't occur ON the surface. Does it occur in the human eye? How? Because I don't thinks the 2 rays will actually hits each other exactly IN the human eye.