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."
... Indus Valley region circa 1500 BCE. There seems to be no clear
evidence that these hordes destroyed the existing Indus Valley culture.
(See Aryan invaders). But it is ...