This applet shows the simplest case of diffraction, i.e., single slit diffraction. You can change the color of the light by draging or clicking the spectrum selector. You may also change the width of the slit by dragging one of the sides.
Diffraction is a phenomenon which envolves the bending of waves around obstacles.
If one maps the intensity pattern along the slit some distance away, one will find that it consists of bright and dark fringes. In the middle a central bright fringe can be found, it is the largest bright fringe. Notice the effect of both the slit width and wavelength by dragging the slit sides and spectrum selector, respectively.