Bragg's law is an equation that predicts the angles at which one will observe coherent scattering (diffraction) from a crystal lattice. It is essentially a special-case of the more general phenomenon of scattering. The law is given by:
where n is an integer, λ is the wavelength of the incident wave (e.g. X-ray or neutron), d is the spacing between the planes in the atomic lattice, and θ is the angle between the incident ray and the scattering planes. The sharp peak that results from the layering in a well-defined realspace lattice is thus often called a Bragg peak.