In general, lightwave travels in a straight line. A very careful study shows that the light will bend when it is passed through and the edge of an obstacle or small opening. "The phenomenon of bending of light around the corners of an obstacle and the spreading into the region of the geometrical shadow is called diffraction." The diffraction of light produces the dark and the bright fringes known as diffraction bands or diffraction fringes. Moreover, diffraction is shown by all kinds of waves. The necessary condition for it is that the size of the obstacle must be comparable to the wavelength of the wave.