Interference Patterns for Light - 3 Factors - showmethephysics.com

The laser light in this demonstration passes through a piece of clear plastic containing very tiny slits that are closely spaced.
When the light wave passes through these slits it produces an interference pattern that consists of alternating bands of bright and dark lines. The right lines come from constructive overlap, the places in between are produced by a destructive overlapping of waves. The spacing between the bright lines are determined by 3 factors - distance between the slits, wavelength of light used and the distance between the slits and the screen.