The Smoking Room at Ickworth House near Bury St Edmunds, Suffolk has been the setting for the research by John Mardaljevic, Professor of Building Daylight Modelling in Loughborough Univesity’s School of Civil and Building Engineering, who has been using high dynamic range (HDR) imaging to measure where the natural light falls at different points throughout the day and over several months.

As is the case with the majority of its historic buildings, the National Trust is keen to balance visitor enjoyment with the preservation of paintings, textiles and furniture that are vulnerable to light fading and ageing.

As a result of his new research, Professor Mardaljevic was able to show 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. He did this 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.

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The ‘contour map’ image = physical measurement of the light level as it falls onto a surface at different points
The ‘luminance map’ image = physical measurement of the brightness of a surface using the HDR imaging

Professor Mardaljevic said that 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.”

Together with the HDR measurement, Loughborough University is using a technique called climate-based daylight modelling to predict how the long-term daylight exposure can change when, for example, opening hours are increased. “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,” said Prof Mardaljevic.

As a result of this research, which was conducted in partnership with Cannon-Brookes Lighting and Design, 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.”

The past 20 years have witnessed a marked reassessment of the function and evaluation of natural illumination in buildings. Professor Mardaljevic will describe these recent advances in his inaugural lecture using illustrations from a diverse collection of projects carried out over the last two decades. The lecture, titled Daylighting of Buildings: 2,500 Years of History / 20 Of ‘Revolution’, will be held in Loughborough University’s Lecture Theatre at 5pm on Wednesday 2 December.

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The Smoking Room, Ickworth House where research into daylight exposure in heritage buildings has taken place. ©LoughboroughUniversity