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."
... Image[?] (MOMI)
National Gallery
National Portrait Gallery
Natural History Museum[?]
Science Museum
Tate Gallery: Tate Britain and Tate Modern
Victoria and Albert ...