Diffraction grating pattern formed by laser light (red). The laser light has passed through an array of crossed gratings. Because light is a wave, and also because the slits in the gratings are narrow enough, the light diffracts (spreads out) after it passes through the grating. This diffracted light then overlaps to produce interference effects that form the pattern seen. Analysis of this pattern can reveal the original structure of the grating through which the light passed. This is the basic principle used in X-ray diffraction, where X-rays are used to study crystal structures where regular array of atoms act as diffraction gratings.