I have read that when a thin film becomes very thin (lambda>>film), it actually does not reflect any light since the incident wave and the reflected wave interfere destructively (and there is no light reflected off the bottom of the film). This would be because the reflected wave is phase shifted by half a wavelength when it hits the top of the film, which has a higher refractive index. It would therefore be perfectly out of phase with the incident ray.
But my question is, wouldn’t this destructive interference happen in the normal case too, even when there is a 2nd reflected wave from the bottom of the film?
Why are we in this case considering the interference of the two reflected waves only, and not the destructive interference with the incident wave?