Diffraction of light is a phenomenon that occurs when any form of wave, including waves of light, attempt to move around small obstacles or through small openings. An example is shown below. In this image you can see the result of waves of light flowing through a slit. Instead of them coming out and continuing the pattern they were following before they exited the slit, more and more waves have to fit their way through a small opening causing a distortion that is sometimes visible.The diffraction effects become less noticeable as the slits become larger, as shown here:
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