The dark side

The Library with its blinds down, at Osterley Park.

The Library at Osterley, with blinds down. (photo by Laura Brooks)

Have you ever visited Osterley House on a beautiful sunny day and wondered why it seemed so dark inside?  Well, this was the theme of the recent taster session held by the house team for its volunteers.

The session explained about Osterley’s origins as a summer house for the wealthy Child family in the 18th century and covered how the house would have been lit historically.  However, what some people didn’t know was why on some days, certain rooms seem too dark.  The reason for this was explained, plain and simply – light.

In the same way that strong sunlight can change the pigmentation of your skin, leaving you slightly browner or, if you’re really unlucky, horribly burnt, light can also affect historic interiors and collections, and cause irreversible damage, such as fading, yellowing and cracking.  So, to try to control the amount of light that enters the house, various measures are taken.  These include the use of shutters and blinds, throughout the house.  Some rooms, such as the Tapestry Room, continuously stay protected from natural light by having their shutters closed, with the only light source in the shape of electric lamps.  Others, such as the Eating Room, may suddenly become quite dark, and need their light levels changed.  For this reason, the house team have to walk round every so often when the house is open, adjusting blinds in different rooms, according to how much light is coming in.

Blue wool dosimeter on Drawing Room carpet, Osterley Park.

Close-up picture of blue wool dosimeter on Drawing Room carpet at Osterley Park (photo by Laura Brooks).

Preventing light damage is not just about pulling down blinds or closing shutters.  It is also about measuring the amount of light the house receives.  Light is measured in ‘lux’.  To see how much lux a room receives, a light meter is used.  Too little lux and a visitor wouldn’t be able to see, causing them to bump into furniture or walk on priceless carpets.  Too much and the collection will start to show signs of damage.  Other forms of monitoring include on-the-spot monitors, which are used on a daily basis, and blue wool dosimeters.  These dosimeters show how much light enters the house each year.  They are placed in a room and at the end of the year, checked to see how much fading has occurred.

As mentioned earlier, how visitors view the house is a consideration.  The recommended amount of light needed for visitors to see is measured at 10 lux.  Additionally, the visitor route is planned out so that visitors are, hopefully, not walking from a bright room into a darker one, although sometimes this cannot be helped.  For example, when walking from the Long Gallery into the Drawing Room, visitors will need to take a minute or two to adjust their eyes so that they can take in the details of Robert Adam’s design.

So, next time you are in Osterley on a sunny day (if we have any more of those this year) and a room seems a bit gloomy, just allow your eyes time to adjust and you will soon see why we are so keen to continue to protect the house’s amazing collection and interiors.

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2 thoughts on “The dark side

    • Thanks for your comment Tony. Osterley follows National Trust standards when it comes to caring for and protecting our collection, including light conservation.

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