Newton's rings appear as a series of alternating bright and dark rings when monochromatic light is incident on a spherical lens in contact with a flat surface.

The intensity variation in the interference pattern for Newton's rings for transmitted light is given by the equation . The intensity of the rings for reflected light is given by the equation , since there is a phase change of after reflection.

Here is the wavelength of light, is the radius of the Newton's rings and is the radius of curvature of the plano-convex lens.