Response of printing coloured ink to light exposure measurement and analysis

Every material changes its colours if it is exposed to light for much time: this event is called photo-damage. The effect depends on the energy and the spectral power distribution of the incident radiation and also on the proprieties to absorb the light and change with it of the receiving material. A new measure is proposed in order to quantify these proprieties. The relative spectral responsivity s(λ)_dm,rel indicates how much a monochromatic radiation centred on wavelength λ contributes at the photo-damage in a specific materials. In this paper a procedure to measure the relative spectral responsivity of coloured material is described and results on printing inks are presented. The knowledge of the relative spectral responsivity s(λ)_dm,rel is helpful to define the ideal spectral emission of the light source which should light an art work with the aim of preserving its colours.