Development of LigthCheck® Ultra: A novel dosimeter for monitoring lighting conditions of highly photosensitive artefacts in museums

This paper presents the development and optimization of an ultrasensitive light dosimeter, especially designed for the preventive risk assessment of damage to highly photosensitive artefacts. This indicator, named LightCheck® Ultra, is composed of a photosensitive dye/polymer layer applied on a paper support. The indicator is characterized by a progressive colour variation as the exposure to light increases. Initially blue, the colour successively changes through purple and pink to white, under the effect of visible light. The colour variation was investigated under different environmental conditions. The light-induced alterations under study were evaluated using various light sources and illuminance levels. The impact of otherfactors unconnected to light (such as temperature, humidity, indoor air pollution - atmospheric and volatile organics - and oxygen) was also studied. The behaviour of the indicator in the field in selected museums and historic houses was assessed in parallel with the laboratory experiments at each development stage. Finally, the calibration was carried out and a reference colour scale was provided for fast and easy reading of the indicator. By means of this reference colour scale, the colour exhibited by the dosimeter after an exposure can be easily correlated to a quantitative indication of the light dose received. The phases of development and testing of this novel light dosimeter are presented in detail, from the early design to the final product.