In optics the Lagrange invariant is a measure of the light propagating through an optical system. It is defined by :

H = n\overliney - nu\overline

, where and are the marginal ray height and angle respectively, and and are the

chief ray 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. Rays are used to model the propagation o ...

height and angle. is the ambient refractive index. In order to reduce confusion with other quantities, the symbol may be used in place of . is proportional to the throughput of the optical system (related to étendue). For a given optical system, the Lagrange invariant is a constant throughout all space, that is, it is invariant upon refraction and transfer. The optical invariant is a generalization of the Lagrange invariant which is formed using the

ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (g ...

heights and angles of any two rays. For these rays, the optical invariant is a constant throughout all space.Optics Fundamentals
Newport Corporation, retrieved 9/8/2011

References

{{Optics-stub Geometrical optics

See also

References