LIGHT CHECK ® Light Dosimeter Strips

LightCheck® is a new tool that enables evaluation of the quantity of light received by an artefact during exhibition even under dim light such as 50 lux for a few months. LightCheck® is made of a light sensitive coating on a substrate. The colour of LightCheck® changes during exposure. A calibration has been established between the colour and the luminous exposure. This colour change is proportional to the luminous exposure although other factors such as temperature, pollutants and type of light (spectral distribution) may have a small effect. The luminous exposure given in the colour reference scale corresponds to the colour changes produced with a continuous exposure under a quartz halogen lamp at 500 lux , 23 °C, 55 % RH.

Damage to cultural heritage caused by light Long or regular exposure to artificial or natural light may cause irreversible damage to objects. This damage may manifest itself as discoloration or fading, or result in a change of a mechanical nature (brittleness…). It is accepted that damage increases with length of exposure and intensity of lighting.

Exposure to light

Rather than determining exposure length in weeks or months (which may not be correct in the case of irregular lighting conditions), it is advisable to monitor the luminous exposure, expressed in lux hours (lx.h), that is to say the quantity of light (called illuminance) multiplied by time of exposure (in hours). This can be achieved using a cumulative data logger, and in the case of natural light, whose characteristics continuously change according to time of day, external weather and location in the exhibition room, a data logger has to be adjacent to each object. This is very often impractical for budgetary, aesthetic or other reasons.

Risk to artefacts Depending on their chemical composition, physical structure, history or climatic environment artefacts may exhibit very different reactions to light exposure. It may happen that visually similar objects react differently from each other when exposed under the same conditions. This makes it almost impossible to predict, without performing specific experiments, how long an object can be exposed with the minimum risk of deterioration. Nevertheless, objects may be grouped roughly into four categories according to their supposed vulnerability to light based on empirical experience. For instance, organic materials, synthetic dyes, textile and graphic documents are more fragile than easel paintings.

Accepted annual luminous exposure limits from published data:

* Luminous exposure values from Appendix 8a, p. 138 of: J. Tétreault, Airborne Pollutants in Museums, Galleries and Archives: Risk Assessment, Control Strategies and Preservation Management, Canadian Conservation Institute, Ottawa, 2003, 168 p.
# A more exhaustive list of artefacts and materials belonging to each ISO category can be found in the manual cited above..

A strip of LightCheck ® is placed close to the artefact in order to get the same light exposure conditions. Every day, week or month depending on light levels, evaluate the Lightcheck by comparison of the colour to the calibration card. Choose the most similar colour, which will give a code i.e. 1S, 2S, 3S, 4S. Use this code to obtain an equivalent luminous exposure (ELE) from the tables below.

To estimate the annual exposure, multiply the ELE figure by 365 and divide by the number of days for which the Lightcheck has been exposed.

If a LightCheck® becomes white, the maximum luminous exposure has been exceeded.

LightCheck® Sensitive "LCS" for more durable objects (Category III acording to the table below)

LightCheck® Ultra "LCU" for light sensitive objects (Category II according to the table below) is no longer produced.

LightCheck® is exposed close to the object and its colour will change depending on the cumulative luminous exposure it receives.

The LightCheck® must be placed in such a position that it will receive the same exposure as the artefact that is under observation / investigation. Equivalent luminous exposure can then be determined by comparison with a coloured reference scale.

LightCheck® is a product of a European Commission funded project "A light dosimeter for monitoring cultural heritage - development, testing and transfer to market" (LiDo, EVK4-CT2000_00016).

WARNING

LightCheck®

• contains dyes that might migrate and produce stains or spots. Do not place in direct contact with an artefact and be aware of volatile organic compounds that may be emitted. Do not touch the surface of the strip.
• is not intended for monitoring high illuminance level such as camera flashes, nor has it been tested for long-term use over years of exposure.
• is not intended for use in an oxygen free environment

Literature: Choi, Y; Marchesi, M: "Innovative tools for exhibition purposes: environmental and damage assessment", Paper Conservation News 112, 2004, p. 12-13.
Bildquelle: Fraunhofer Institut für Silicatforschung Würzburg www.isc.fraunhofer.de

Further publications for LightCheck click here.

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