temperatures as calculated from the planet's radiative equilibrium with all of space. By 1900 Max Planck empirically derived a generalized law of blackbody radiation, thus clarifying the emissivity and absorptivity concepts at individual wavelengths. Other radiometric coefficients See also Albedo Black-body radiation Passive daytime radiative cooling Radiant barrier Reflectance Sakuma–Hattori equation Stefan–Boltzmann law View factor Wien's displacement law References Further reading An open community-focused website & directory with resources related to spectral emissivity and emittance. On this site, the focus is on available data, references and links to resources related to spectral emissivity as it is measured & used in thermal radiation thermometry and thermography (thermal imaging). Resources, Tools and Basic Information for Engineering and Design of Technical Applications. This site offers an extensive list of other material not covered above. Physical quantities Radiometry Heat transfer