BS ISO 9416:2017

1   Scope This document specifies a method for the calculation of light-scattering and light-absorption coefficients based upon diffuse reflectance measurements made under the conditions specified in ISO 2469 using the colour matching function

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            and CIE illuminant C. 
It is emphasized that the strict evaluation of the light-scattering and  light-absorption coefficients  requires conditions which cannot be achieved with the instrumentation specified here.
  The values obtained by application of this document are dependent on the application
  of the Kubelka-Munk equations, not to full reflectance data but to  reflectance factor  data obtained using the specified d/0° geometry and a gloss trap. 
The use of the method is restricted to white and near-white uncoated papers with an
  opacity less than about 95 %. Paper that has been treated with a fluorescent dyestuff
  or that exhibits significant fluorescence can only be dealt with if a filter with
  a cut-off wavelength of 420 nm is used to eliminate all the fluorescence effect in
  the UVex(420) mode. 

    NOTE 1  The residual UV-level in the instrument may depend on whether the instrument is adjusted
     to UV(C) or UV(D65) conditions prior to switc...