The net effect of scattering from a single row is equivalent to partial reflection from a mirror imagined to be aligned with the row. For constructive interference this must be an integer number of wa...The net effect of scattering from a single row is equivalent to partial reflection from a mirror imagined to be aligned with the row. For constructive interference this must be an integer number of wavelengths, m \lambda, where the integer m is called the order of interference. This sharpening of the peaks as the number of rows increases is very similar to the sharpening of the diffraction peaks from a diffraction grating as the number of slits increases.
