Hello, I have the following question: Physics books say that in order to see diffraction you need a wave to encounter an object that is comparable in size to the wavelength. This is presumably the reason why light does not bend through an opened door but sound does. My question is, what happens to Huygens Principle in the light scenario? If we can always consider the wavefront as another light source, wouldn't this mean that when light encounters ANY slit, no matter its size, the light will spread out in all directions? Does Huygens Principle simply not apply in some cases?? Thank you.