Before revision: Light rays in Luneburg's theory are defined as trajectories orthogonal to the discontinuity surfaces and with the right parametrisation they can be shown to obey Fermat's principle of least time thus establishing the identity of those rays with light rays of standard optics.
After revision: Light rays in Luneburg's theory are defined as trajectories orthogonal to the discontinuity surfaces and can be shown to obey Fermat's principle of least time thus establishing the identity of those rays with light rays of standard optics.