The diffraction pattern from a hexagonal–shaped hole. Note the six–fold symmetry of the pattern. Observation of such complex patterns can reveal the underlying symmetry structure of the object that diffracts the light.
The phenomenon of diffraction can be readily explained using Huygen's principle: When the wavefront of a light ray is partially obstructed, only those wavelets which belong to the exposed parts superpose, in such a way that the resulting wavefront has a different shape.
This permits bending of light around the edges. Colourful fringe patterns are observed on a screen due to diffraction. It can also be termed as the breaking up of an electromagnetic wave as it passes a geometric structure (e.g., a slit), followed by reconstruction of the wave by interference.
If the wavelength of light is much smaller than the aperture or slit width, a light wave simply travels onward in a straight line after passing through, as it would, if no aperture were present. However, when the wavelength exceeds the size of the slit, diffraction of the light occurs, causing the formation of a diffraction pattern consisting of a bright central portion (the primary maximum), bounded on either side by a series of secondary maxima separated by dark regions (or minima). The maxima and minima are created by interference of diffracted light waves.