The goniospectrophotometer GEFE, designed and developed at IO-CSIC (Instituto deÓptica, Agencia Estatal Consejo Superior de Investigaciones Científicas), was conceived to measure the spectral Bidirectional Reflectance Distribution Function (BRDF) at any pair of irradiation and detection directions. Although the potential of this instrument has largely been proved, it still required to be upgraded to deal with some important scattering features for the assessment of the appearance. Since it was not provided with a detector with spatial resolution, it simply could not measure spectrophotometric quantites to characterize texture through the Bidirectional Texture Function (BTF) or translucency through the more complex Bidirectional Scattering-Surface Reflectance Distribution Function (BSSRDF). Another requirement in the GEFE upgrading was to provide it with the capability of measuring fluorescence at different geometries, since some of the new pigments used in industry are fluorescent, which can have a non-negligible impact in the color of the product. Then, spectral resolution at irradiation and detection had to be available in GEFE. This paper describes the upgrading of the goniospectrophotometer GEFE, and its new capabilities through the presentation of sparkle and goniofluorescence measurements. In addition, the potential of the instrument to evaluate translucency by the measurement of the BSSRDF is briefly discussed.
Coatings with diffraction pigments present high iridescence, which needs to be characterized to describe their appearance. The spectral Bidirectional Reflectance Distribution Function (BRDF) of six coatings with SpectraFlair diffraction pigments were measured using the robot-arm-based goniospectrophotometerer GEFE, designed and developed at CSIC. Principal Components Analysis (PCA) has been applied to study the coatings' BRDF data. From data evaluation and based in theoretical considerations, we propose a relevant geometric factor to study the spectral reflectance and color gamut variation of coatings with diffraction pigments. At fixed values of this geometrical variable, the spectral BRDF component due to diffraction is almost constant. Commercially-available portable goniospectrophotometers, extensively used in several industries (automotive and others), have to be provided with more aspecular measurement angles to characterize goniochromatic coatings based on diffraction pigments.
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