This ray is useful, because it crosses the optical axis again at the locations where an image will be formed.

The marginal ray (sometimes known as an a ray or a marginal axial ray) in an optical system is the meridional ray that starts at the point where the object crosses the optical axis, and touches the edge of the aperture stop of the system.

Such rays do not cross the optical axis anywhere, and are not parallel to it.

A skew ray is a ray that does not propagate in a plane that contains both the object point and the optical axis.

A meridional ray or tangential ray is a ray that is confined to the plane containing the system's optical axis and the object point from which the ray originated.

Simple ray diagram showing typical chief and marginal rays If the material is birefringent, the refracted ray may split into ordinary and extraordinary rays, which experience different indexes of refraction when passing through the birefringent material.Conservation of energy requires that the power in the incident ray must equal the sum of the power in the refracted ray, the power in the reflected ray, and any power absorbed at the surface. The angle between this ray and the normal is known as the angle of refraction, and it is given by Snell's Law. The refracted ray or transmitted ray corresponding to a given incident ray represents the light that is transmitted through the surface.The Law of Reflection says that for a specular (non-scattering) surface, the angle of reflection is always equal to the angle of incidence. The angle between the surface normal and the reflected ray is known as the angle of reflection. The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface.The angle between this ray and the perpendicular or normal to the surface is the angle of incidence. An incident ray is a ray of light that strikes a surface.These are defined and described below, grouped by the type of system they are used to model.Дiagram of rays at a surface, where Оё i is the angle of refraction. There are many special rays that are used in optical modelling to analyze an optical system. Rays from each object point can be mathematically propagated to locate the corresponding point on the image.ДЄ slightly more rigorous definition of a light ray follows from Fermat's principle, which states that the path taken between two points by a ray of light is the path that can be traversed in the least time. Objects to be imaged are treated as collections of independent point sources, each producing spherical wavefronts and corresponding outward rays. Geometric optics describes how rays propagate through an optical system. They bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Light rays in homogeneous media are straight. Some wave phenomena such as interference can be modeled in limited circumstances by adding phase to the ray model.ДЄ light ray is a line ( straight or curved) that is perpendicular to the light's wavefronts its tangent is collinear with the wave vector. Ray optics or geometrical optics does not describe phenomena such as diffraction, which require wave optics theory. 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. This allows even very complex optical systems to be analyzed mathematically or simulated by computer. 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. In optics a ray is an idealized geometrical model of light, obtained by choosing a curve that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow.

Not to be confused with Incident Light (film).

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