Spotlight on light

A painting at Petworth lit by LED lights

10% of natural light from the sun is made up of ultra-violet (UV) radiation. UV light is the type used in sun beds and causes sun burn and freckling on our skin but did you know UV light can also damage objects?

What objects are in danger?

UV light particular affects textiles, natural dyes, paints or inks, paper, wood and glues, photographs, varnishes and lacquer where it rots fibres and fades colour. Heat from sunlight can also make surfaces expand, crack and dry.

How much light is dangerous?

Light is measured in 'lux' units and 1 lux equals the illumination of a surface one metre away from a single candle.

To put this into context, depending on the day, sunlight can range between 32,000 and 100,000 lux but 50 to 100 lux is the maximum amount of light allowed for sensitive materials like textiles wihtout causing irreversible damage.

What do we do to protect items?

As you wander the state rooms of the mansion at Petworth, you might notice blue fabric in a rectangle slide placed on some of our items. These are blue wool dosimeters and measure UV radiation. Every year we analyse the wool to see if the colour has faded and this forms part of a light plan to keep all 4,500 items in the collection and the rooms within a safe quota of light.

Some items are more sensitive to light than others and during closing we cover these objects with thick blake cloths and take these off just as we open to ration the amount of light these objects receive

Some rooms receive more light than others because of windows and the direction of the sun so this it does mean to protect our collection for future generations we do close some drapes and shutters and use UV filter films on our windows.

How can you help?

Over the summer of 2017 we are testing the use of artificial lights in some of the state rooms. These LEd spotlights don't emit any UV light and don't give out any heat.

By becoming a member your support helps us to purchase more LED we can use to light the collection. You can also volunteer with us to help monitor and record our light levels.