Development of LightCheck Ultra: a novel dosimeter for monitoring lighting conditions of highly photosensitive artefacts in museums

Abstract

be clearly distinguishable by simple visual examination, so that a simple reading can be made on site with no specific measuring equipment. Dosimeters usually provide a very simplified model and, in reality, their response function cannot be expected to reproduce exactly that of artefacts under the same conditions. Rather, the sensor should be used for semi-quantitative indications by ensuring that its behaviour can suitably simulate the reaction under analysis (e.g. discolouration or corrosion). In this research, the environmental factor under examination was light, and the sensors developed were specifically tailored to respond to the damaging effects of light. Light induces photochemical reactions in materials which may result in a change in the appearance of objects (e.g. fading or chromatic balance) [1]. It is well established that any unnecessary light exposure should be avoided for art objects and archival materials on display [2]. Moreover, it has to be taken into account that these reactions can also be modified or accelerated by other environmental parameters such as temperature, humidity, external atmospheric and indoor air pollution 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 other factors 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.

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