National Trust balances daylighting for preservation and visitors

The National Trust is considering revising daylighting guidance for its historic houses following a research project looking at how to preserve precious house contents and keep them on display to visitors.

Research by Loughborough University and Cannon-Brookes Lighting and Design looked at the distribution of natural light and its level of exposure, using high dynamic range (HDR) imaging to measure where the natural light falls at different points in the day and over months in the Smoking Room in Ickworth House in Suffolk. The National Trust wanted to balance visitor enjoyment with the preservation of paintings, textiles and furniture that are vulnerable to light fading and ageing.

The research showed the distribution of light exposure across all surfaces which were of interest in the rooms, so that a comprehensive evaluation could be made of the illumination conditions over long periods of time. This was done with the help of a camera tethered to a computer that controls a sequence of exposures which occur every 10 minutes. These exposures were then converted into physical measures of the light level as it falls onto a surface at different points.

John Mardaljevic, professor of building daylight modeling at Loughborough said: “In any heritage building the light will vary across the walls depending on the arrangement of windows and the time of day. This is the first time, however, that we have been able to use HDR in a heritage setting to create a cumulative luminance image, from which a physical measure of illumination exposure across the camera’s wide-angle perspective is derived.

Climate-based daylight modeling is being used to predict how the long-term daylight exposure can change when, for example, opening hours are increased. Mardaljevic added, “Used together, these two techniques are a great way of better understanding natural light, especially at a time when historic houses are being encouraged to extend access and opening hours where possible.”

The National Trust is looking into the feasibility of revising the daylight management guide for its historic houses, which takes into consideration the scheduling of the use of shutters/blinds in each of the rooms. Dr Nigel Blades, preventive conservation adviser at the National Trust, said: “The research is enabling the National Trust to understand better than ever before, the fall of daylight onto light sensitive surfaces in historic showrooms.

“We are learning how the daylight received accumulates through the days and seasons of the year. This knowledge will enable us to understand the impact of extended opening hours on light exposure. Based on the research, we will fine tune our use of daylight to minimise the rate of change in light sensitive objects, while providing sufficient daylight for visitors to enjoy our collections.”

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