Diffraction from a large three-dimensional periodic structure such as many thousands of atoms in a crystal is called Bragg diffraction. It is similar to what occurs when waves are scattered from a diffraction grating. Bragg diffraction is a consequence of interference between waves reflecting from many different crystal planes. The condition of constructive interference is given by Bragg's law : m λ λ = 2 d sin ⁡ ⁡ θ θ , where λ λ is the wavelength, d is the distance between crystal planes, θ θ is the angle of the diffracted wave, and m is an integer known as the order of the diffracted beam.