In Optics Fundamentals

Newport Corporation, retrieved 9/8/2011

optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultra ...

the Lagrange invariant is a measure of the light propagating through an optical system. It is defined by
:$H\; =\; n\backslash overliney\; -\; nu\backslash overline$,
where and are the marginal ray height and angle respectively, and and are the chief ray 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 heights and angles of any two rays. For these rays, the optical invariant is a constant throughout all space.Newport Corporation, retrieved 9/8/2011

See also

* Etendue * Smith-Helmholtz invariant * Abbe sine conditionReferences

{{Optics-stub Geometrical optics