Spotlight on darkness at Erddig

Sometimes the rooms in the house appear darker than you might have your rooms at home and you may have to stand a little closer to the windows to read our written information or take some time to allow your eyes to adjust.

Why does the house at Erddig sometimes 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 our collection, while still helping visitors to experience this wonderfully eclectic home.  As an accredited museum, one requirement is that we care properly for the items in our collection, 30,000 in all and the second largest in the National Trust. Minimising deterioration and conserving our collection for future generations to enjoy is a big part of our work at Erddig and sunlight is one of the main causes of damage at Erddig.

Discover an atmospheric house above and below stairs
Wooden towel stand in the Blue Bedroom containing the most striking examples of historic textile colour fade
Discover an atmospheric house above and below stairs

Have you ever noticed how photographs facing a window at home fade quickly?  This is because the light that allows us to see 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 the taxidermy) fades and breaks down.  This damage is not only cumulative but irreversible.

How we limit light damage?

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 per year in these spaces.  The average human eye needs no more than about 150 lux (a measure of brightness) to see acceptably; anything higher than this brightness makes little impact on our ability to see, but has a massive impact on fragile, light-sensitive objects. – more energy being absorbed with no gain for us.  

Discover John Meller's fine furniture and furnishings
Erddig Saloon in John Meller's rooms of parade
Discover John Meller's fine furniture and furnishings

So to maintain 150,000 lux hours in a year, we need to limit the opening hours of the rooms to 1,000 each year.  This is why our opening times are relatively short since moving to seven-day opening, in comparison with some other properties; it’s the high light sensitivity of what’s on display at Erddig.  So the crudest method we have for limiting light damage is by keeping the rooms in complete darkness for as long as possible, only opening shutters and blinds minutes before visitors enter.

100 Blinds

During opening hours we try to manage the effects of light damage in a number of other ways.  The most damaging light, ultra-violet, is kept out of the rooms completely by applying a special film to the window panes.  It is often this film coming to the end of its 10-15 year lifespan which causes a rippling effect, rather than the original nature of the historic glass.

One of the jobs that keeps the conservation team busy is adjusting the blinds to control the amount of visible light in a room depending on the brightness of the sun.  We have around 100 blinds throughout the house and many of them need to be adjusted regularly to block out the sun’s damaging rays when it’s bright but also raised when it’s dull outside so that visitors are able to see the rooms and our collection.


The Library at Erddig
The Library at Erddig
The Library at Erddig


Throughout the house you may notice little pieces of card with blue fabric inside. These are dosimeters and we use them to measure annual light exposure in sensitive areas and on sensitive items, like the boulle cabinet in the saloon.  The dosimeters are placed where we want to measure the light level and then at the end of the year they are sent off 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, which allows us to review how we’re managing light in that area over a whole year.

Light work

Our conservation team also takes spot readings on a daily basis.  We undertake large light monitoring exercises to collect data to be analysed to allow for more informed room plans, showing the areas in a room that receive the most light in relation to windows and blind positions.  This data is consolidated with other light readings to help us determine annual light exposure estimates for sensitive areas that are not monitored with a dosimeter.

So, when you come to Erddig you can be sure that we’re doing our bit as part of the country’s largest conservation charity to care for the house and its collections for ever, for everyone and by coming here to step back into the past, you’re helping us preserve this special home’s future.