Light control as a contribution to climate protection in historic buildings. Model study of the effect of different light control systems on historic buildings.

The issue of light protection is of significant importance in the conservation of art and cultural heritage, particularly in the context of historic buildings. However, it has not yet received the level of attention that it merits. In the optimal scenario, light protection entails the safeguarding of light-sensitive furnishings, including tapestries, wallpaper, paintings, and plastics, while simultaneously reducing the influx of solar energy, which contributes to an increase in interior temperature. In addition to the visual and ultraviolet ranges of the electromagnetic spectrum, sunlight also contains infrared wavelengths. The latter is an important factor in the challenges posed by anthropogenic climate change, with a high potential for damage. The effects of IR radiation cause interior temperatures to rise, which can lead to accelerated chemical reactions in historic material composites. This results in accelerated ageing or deterioration of our cultural heritage. This can be remedied either by energy-intensive cooling technology or by passive measures such as light protection, which is the focus of the proposed project.

Optical radiation can result in three distinct forms of damage. On the one hand, optical changes, including fading, chalking, colour changes and other alterations to the appearance of the material, occur as a result of exposure to visual light and other forms of radiation, such as UV and IR radiation. These changes can potentially lead to irreversible damage. Conversely, optical radiation, particularly UV radiation, can result in structural damage that ultimately leads to the complete loss of substance over time. To date, there has been a paucity of research conducted into this latter area, largely due to the fact that the requisite material tests cannot be carried out in a non-destructive manner. Furthermore, infrared radiation can cause thermal heating of cultural assets when it interacts with surfaces in a localized manner. Such exposure can result in structural alterations. For instance, when the sun traverses the surface of a given object over the course of a day, localized heating may occur. This can, in turn, give rise to changes in the material composition of the object, such as the movement of paint flakes. Over time, this cyclical movement/stress can lead to further material changes and, in extreme cases, even breakage or loss.

In contemporary museums, the issue of light protection is frequently considered during the development of a lighting concept. In the past, historical buildings frequently exhibited protective measures, such as curtains on paintings, covers for furniture, shutters, and so forth. The shift in usage patterns, with daily openings instead of the earlier irregular use, often necessitates individual light protection, even in listed buildings. In churches, in particular, this has been increasingly implemented in recent decades.
 
A number of questions pertaining to the protection of listed buildings from light pollution remain unanswered, and further research is required to address these issues:

• What parameters should be taken into account when tendering for efficient light protection?
• The question thus arises as to how this can be installed in historic buildings in a way that is compatible with listed buildings.
• It is necessary to determine the optimal distance between the light protection and the window in order to protect the original glazing from condensation and/or overheating, while allowing sufficient daylight into the interior.
• It would be beneficial to ascertain the long-term stability of light protection systems due to their exposure to the sun. Currently, only reports from property managers are available, which do not provide sufficient data. The identification of materials that fade quickly or require the installation of UV protection is crucial for informed decision-making regarding the sustainability of these systems.

In order to address the research gap concerning light protection on listed buildings, the project will investigate a range of light protection methods. These will include UV/IR protective films, tinted glass that can be added in front of the original glazing, and curtains/screens. The aim is to compare and evaluate these in terms of their effectiveness in protecting the object, their visual impact, and their ability to reduce solar input and prevent damage.
The objective of the project is to develop strategies for the long-term protection of monument furnishings from damage caused by light. The implementation of appropriate light protection measures will ensure the preservation of valuable cultural assets, while stabilising the indoor climate in response to rising temperatures and solar radiation can enhance energy efficiency and reduce CO2 emissions. The interdisciplinary project aims to investigate practical solutions through the integration of systematic laboratory tests and the analysis of diverse case studies.