Powdered materials readily diffuse, absorb and scatter light which falls on them and in order to obtain accurate and consistent spectrophotometric measurements it is necessary to use well controlled standard colorimetric procedures. The point is the spectra in question specifically represent the variation of light absorption relative to spectral wavelength and it is necessary to maintain the effects of diffusion and light scattering as well defined constants of the procedure. The CIE (Commission Internationale de Le’clairage) publication ‘Technical Report CIE 15:2004 Colorimetry’ sets out in detail the relevant standards and methodology.

Thanks Dr. David Oulton