In
optics a
ray is an idealized model of
light, obtained by choosing a line that is perpendicular to the
wavefronts of the actual light, and that points in the direction of energy flow. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of
ray tracing. This allows even very complex optical systems to be analyzed mathematically or simulated by computer. Ray tracing uses approximate solutions to
Maxwell's equations that are valid as long as the
light waves propagate through and around objects whose dimensions are much greater than the light's
wavelength. Ray theory does not describe phenomena such as
interference and
diffraction, which require
wave theory (involving the relative
phase of the rays).