Transparent medium with angular-selective transmitting or reflecting properties

A transparent medium as functional surface in regulating heat balance below said surface, said medium comprising glass, a varnish, an aqueous lacquer, a plastic, a plastic film, a transparent polymer, a ceramic, a thermoplastic, or a binder, and pearl lustrous pigments having angle-selective reflection and/or transmission properties wherein the proportion of the solar transmission level in summer at an angle of incidence of solar radiation from 55 to 70° to the solar transmission level in winter at an angle of incidence of solar radiation from 5 to 20° is in the range of 50 to 85%, and wherein said medium acts as functional surface in regulating heat balance below said surface.