Hannelore Römich
Head of working group 'Research for Conservation' at Fraunhofer ISC

Graham Martin
Head of Science, V&A Museum

Bertrand Lavedrine
Director of CRCDG

Mauro Bacci
Head of Research, Istituto di Fisica Applicata "Nello Carrara" (IFAC)

Long or regular exposure to light, artificial or natural, may cause irreversible damage to valuable heritage objects. This damage may be visible, such as discolouration or fading, or result in a change of a mechanical property (e.g. brittleness of the historic material). It is known that the damage increases with the length of exposure and the intensity of lighting.

Rather than limiting the time of exposure for each object, which may be not significant in case of irregular lighting conditions, it is advisable to monitor the lighting during exposure. That can be achieved by using a cumulative data logger. In the case of natural light, whose characteristics continuously change according to the time of day and the location in the exhibition room, a data logger has to be set right adjacent to each object. A continuous monitoring program for various objects would be rather expensive and applicable only for selected examples.

As an alternative LightCheck® is introduced as a new early warning system for preventive conservation, which allows the evaluation of the quantity of light received by an artefact during exhibition. A strip of LightCheck® is placed close to the artefact in order to get the same light exposure conditions (figure 1). Regularly (after some days, weeks, months…) the strip is evaluated by comparison to the corresponding colour scale (figure 2). That can be related to an equivalent luminous exposure. For objects with different sensitivity further action for better protection can be recommended.

Figure 2. Evaluation of the fading rate of the dosimeter (type LCS) Photography by Fraunhofer ISC (click image for larger version)

LightCheck® is made of a light sensitive coating on a substrate. The colour of LightCheck® changes during exposure to light. A calibration has been established between the colour and the luminous exposure. The luminous exposure given in the colour reference scale corresponds to the potential damage of the lighting conditions on site.

Two LightCheck® strips have been introduced, one to monitor the exhibition of light sensitive objects (and short exposure times): LightCheck® Ultra "LCU" and the other one for the more durable objects (and longer exposure times): LightCheck® Sensitive "LCS". The range of sensitivity is explained in figure 3, compared with the more durable blue wool standard (BWS). BWS was developed for industrial purposes and has been the only commercially available light dosimeter so far. Its application in museums was limited because of the low sensitivity to museum lighting conditions.

LightCheck® is a product developed within a project funded by the European Commission (Key action "The City of Tomorrow and Cultural Heritage", reference EVK4-CT2000-00016). The interdisciplinary project team consists of partners from museums (V&A, London), local authorities (SUPP, Prague), industry (Kockott UV-Technik, Hanau) and research institutes (CRCDG, Paris, IFAC, Florence and Fraunhofer ISC, Bronnbach).

Figure 3. Range of sensitivity for LightCheck Ultra (LCU) (click image for larger version)

The marketing will be taken over by Particle Technology, UK. The excellence of the project was duly recognised by being awarded "Pan-European Grand Prix for Innovation" in Monaco in December 2003.

Further information can be obtained through the web-site: www.lido.fhg.de