Abridged Gonio-Reflectometer

The appearance depends on the reflectance for any incident light and at any direction of view, i.e. on the bidirectional-reflectance-distribution function, therefore a gloss measure is only a partial information on the appearance. At least seven definitions of gloss factor exist related to different application fields. We have realized an abridged gonioreflectometer , i.e. an instrument with six different illuminating directions and six directions of view, which are symmetrical to the six illuminating directions. All these directions belong to a plane orthogonal to the analyzed surface. The illumination is produced by narrow band light, as that of LEDs emitting in the medium-long wavelength region. This choice is based on the fact that the gloss appearance is mainly produced by the surface roughness/smoothness and by the Fresnel’s reflection, which depends on the surface refraction-index. Three quantities can be measured with regard to the 6x6 directions considered: 1) the gloss factor, 2) the gonio-reflectance factor, 3) the gonio-reflectance. The calibration of the instrument needs two reflectace tiles, i) one tile constituted by a black glass with known refraction index, whose specular reflectance is defined by the Fresnel law; ii) a second tile with a matt white surface, possibly lambertian, whose gonio-reflectance factor must be certified by a metrological laboratory. Keyword: gloss, gloss factor, reflectance factor, gonio-reflectance