Hi I hope this is the right place to post. I have some questions regarding EM wave amplitudes. There are some other posts in the past regarding this and some people replied by saying that amplitude of a light wave is equal/close to wavelength of the wave. This is deduced from the fact that light wave with a certain wavelength does not pass through holes smaller than the wavelength, so the amplitude should be somewhat near. If this is even approximately true, then linear wave equation should not be valid for light waves since its derivation assumes small displacements/gradients in the transverse direction. For large amplitudes relative to wavelength, the displacement gradient can reach large values. Of course i must be missing something here, E0 and B0 do not have length units, or do they? Any ideas?