Formal Quantum Theory of Light Rays

It is shown that the relation between ray optics and wave optics is analogous to the relation between the classical mechanics of a point particle and quantum mechanics. The time coordinate of quantum mechanics has to be replaced with a length coordinate and the light wavelength λ takes the place of Planck's constant h. A well-known result of quantum mechanics is that it coincides with classical mechanics in the limit h → 0. Correspondingly, wave and ray optics must coincide in the limit λ → 0.