Graininess appearance of goniochromatic samples in lighting cabinets

In 2013 the European Metrology Research Program (EMRP) funded a 36 months research project, "Multidimensional Reflectometry for Industry, xD-Reflect", to investigate the macroscopic optical properties related to visual appearance of modern surfaces. During the three years duration of the project, over in August 2016, several visual experiments have been performed to investigate appearance of materials with goniochromatic and sparkling effects. Metal-flakes produce shiny effects whose definitions, quantities and metrological characterizations are still under development. This paper relates to the measurement and visual estimation of graininess and brightness perceived of metal flakes achromatic pigments materials. The subjective ranking on graininess and brightness of three different sample sets different for particles shape (silver dollar and corn-flakes) and dimension, were compared under similar viewing conditions on two commercial lighting booths, one based on LED lighting and one on fluorescent light, both reproducing CIE D65 illuminating conditions. The subjective rankings were compared with the graininess measured with a Byk-Mac instrument and the luminance measured with a luminancemeter in the experimental conditions inside both lighting booths. The performances of the two lighting cabinets and of the two different flake shapes were also compared. The results are useful both for shops lighting arrangements and industrial panelist investigations.