Optical characteristics and visual appearance for artwork materials

The aim of this study is to evaluate experimentally how well available metrics are able to evaluate how lighting sources affect the perception of visual attributes of artworks exhibited, providing useful indications for works of art exhibition designers. The study considers objective investigations on optical material properties (i.e. spectral reflection factor) compared to subjective tests on colour attributes evaluation of artworks lighted by common lamps (incandescent and fluorescent lamps) and LED lighting sources. Commission International Eclairage (CIE) developed several mathematical methods to predict colour rendering of lighting source, as well visual attributes of materials, but are only an approximation of the material appearance: too many parameters of influence, subjects expectancy included, influence the appearance. In artwork exhibition visual appearance is of fundamental importance and currently no reliable and robust appearance model is available. Comparing objective evaluations and subjective results for lighting set up comparable to works of art exhibition, will provide useful indications on the applicability of colorimetric calculation to artwork exhibition when LED are involved. Visual attributes (hue, saturation, brightness..) of six different colours under LED and not-LED sources at the same Correlate Colour Temperature were compared to the associate objective characteristics calculated from the spectral reflectance. The results show that the perception of visual attributes differs from objective data when SSL sources are involved and when colours are perceived in complex samples: in some cases the visual system is not coherent with the suggestions arising from the calculations.