Diffraction methods, interpreted loosely, could be applied to the techniques of wide-angle X-ray scattering, small-angle X-ray scattering, electron diffraction, small-angle neutron scattering, small-angle light scattering and reflectometry. Each of the above techniques is defined by the size range explored and the property that causes the scattering. Both X-ray and electron diffraction methods depend on the electron density of the sample to produce a signal, light scattering is generated by variations of polarisability (and hence refractive index) in the sample, and neutron scattering requires a difference in scattering length density (vide infra) for scattering to be observed.