Bragg diffraction occurs when radiation, with a wavelength comparable to atomic spacings, is scattered in a specular fashion by the atoms of a crystalline system, and undergoes constructive interference. For a crystalline solid, the waves are scattered from lattice planes separated by the interplanar distance "d". When the scattered waves interfere constructively, they remain in phase since the difference between the path lengths of the two waves is equal to an integer multiple of the wavelength. The path difference between two waves undergoing interference is given by 2"d"sin"θ", where "θ" is the glancing angle (see figure on the right, and note that this differs from the convention in Snell's law where "θ" is measured from the surface normal). The effect of the constructive or destructive interference intensifies because of the cumulative effect of reflection in successive crystallographic planes ("h,k,l") of the crystalline lattice (as described by Miller notation). This leads to Bragg's law, which describes the condition on "θ" for the constructive interference to be at its strongest: