Our work in the house at Erddig

A man wearing glasses stands reading at a brightly lit windowsill, while the surrounding room is dim. — At Erddig you may need to move to the window to read information | © National Trust Images/Vicki Coombe

Erddig’s collection of 30,000 items is the second largest in the National Trust. Minimising deterioration and conserving the collection for future generations to enjoy is a big part of our work in the house, where sunlight is one of the main causes of damage. We work hard to measure and limit light damage, using specialist techniques – and adjusting more than 100 blinds.

Why does the house at Erddig seem dimly lit?

It’s the question we get asked the most. It's partly because we feel that universal electric lighting would go against the decision of the Yorke family not to introduce electricity to the house they owned up until 1973.

But more importantly, our rooms are set up this way to help preserve the collection while still allowing visitors to experience this eclectic home.

Sometimes the rooms appear darker than you might be used to at home, so you may have to stand a little closer to the windows to read information, or take some time to allow your eyes to adjust.

A woman wearing blue protective gloves dusts a lamp suspended from the ceiling. She is using a cleaning brush and a vacuum cleaner. — We’ve deliberately kept electric light at Erddig to a minimum | © National Trust Images/Arnhel de Serra

How can light damage a historic collection?

Have you noticed how photographs facing a window at home fade quickly? This is because the light causes deterioration of the pigments in the ink and the colour then becomes bleached.

This happens to most materials found within Erddig – wood changes colour and becomes brittle, textiles fade and disintegrate and natural history (like taxidermy) fades and breaks down. This damage is not only cumulative, but irreversible.

Minimising light damage at Erddig

All but one of the rooms in the house are classified as ‘highly light sensitive’ due to their decoration and contents. This means that we need to limit total light exposure to fewer than 150,000 lux hours (a measure of brightness) per year in these spaces.

The average human eye needs no more than about 150 lux to see acceptably. Anything brighter makes little impact on visibility, but has a massive impact on fragile, light-sensitive objects. Precious items would absorb more energy, with no gain to our visitors.

Shorter opening hours

The simplest way to limit light damage is to keep the rooms in complete darkness for as long as possible, limiting visiting hours and only opening shutters and blinds minutes before visitors enter.

To keep to 150,000 lux hours in a year, we only open Erddig’s rooms for 1,000 hours annually.

Controlling light levels when we’re open

We keep out the most damaging light – ultraviolet – by applying a special film to the windowpanes. If you see a rippling effect on the glass it’s often this film coming to the end of its 10- to 15-year lifespan, rather than the original nature of the historic glass.

The conservation team are kept busy throughout the day adjusting Erddig’s 100 blinds to control the amount of visible light in a room. Blinds block out the sun’s damaging rays when it’s bright, but also need to be raised on overcast days so that visitors can see and enjoy the rooms.

Three children stand in front of a sunlit window, which has a cream-coloured blind pulled halfway down. — Blinds help control light levels in the house | © National Trust Images/Oskar Proctor

Measuring light levels

Dosimeters

Throughout the house you may notice little pieces of card with blue fabric inside. These are dosimeters used to measure annual light exposure in sensitive areas and on sensitive items, like the boulle cabinet in the Saloon.

At the end of the year we send the dosimeters to a laboratory, where the fading on the blue fabric is compared with that of a known sample. This gives us an accurate reading of the light exposure, so we can review how we’re managing light in that area over a whole year.