In telecommunication, a conservation of radiance is a basic principle of optics, that no passive optical system can increase the quantity L /n2, where L is the radiance[?] of a beam and n is the local refractive index.
Note:"Conservation of radiance" was formerly called "conservation of brightness" or the "brightness theorem."
... 1488. The earliest German translation was
made in 1434 by J. de Bellorivo and is preserved
in Cologne. The editions in German began at
Augsburg in 1486. The first ...