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."
... The earliest of the Vedas, the R^igveda, was composed in the middle of the second millennium BC. The Vedic form survived until the middle of the first millennium BC. ...