Agent of Deterioration #4: Light, UltraViolet, Infrared

As a summer conservation series, we will be talking about the Agents of Deterioration as defined by the Canadian Conservation Institute (CCI) in Ottawa.  If you want to learn more about CCI, see their website or our April 29th blog post.  

This week we are talking about our fourth Agent of Deterioration, Light.  Light doesn’t just cover visible light, we need to be concerned with the light that cannot be seen as well; this includes Ultra Violet (UV) light and Infrared (IR).  Just as our own eyes need to be protected from all forms of light, so do our artifacts. 

A diagram from CCI outlining the wavelengths and energy of different types of light

Typically, it is visible light that fades (or bleaches) colours.  This light would come from the sun shining directly into your museum. UV light will not only fade colours but it will cause “yellowing, chalking, weakening, and/or disintegration” of your objects.  UV light not only comes from the sun but also comes from some sources of artificial lighting, such as fluorescent.  IR light heats the surface of objects, which then leads to the same conditions as Incorrect Temperature (Remember that? Learn all about it here). IR light comes from the sun as well as Incandescent lighting.

So, if these forms of light damage our collections, what should we do!?

Firstly, know what your situation is.  Measure how much visible light is acting upon your objects; to do this you can use a light meter.  Light is measured in lux.  CCI has made this handy chart to show us what we can see with the amount of light we have. 

This chart helps us see why museums tend to want to keep light levels low. Conservators like to keep the most sensitive objects around 50 lux.  However, a balance is needed to be struck between conservation and visibility for visitors.  

To measure UV light, we use a UV meter.  UV light is measured in microwatts per lumen (μW/lm).  CCI recommends that you keep UV levels below 75 μW/lm.

Next, implement controls on the amount of light that is impacting your collection.  If you already know that visible light is coming in, prevent that; this means that you find ways to block the sun from entering your building. This could mean putting up blind or curtains and possibly UV filters on the windows or on lights that emit significant amounts. Controlling the amount and intensity of of the artifical light that is in your museum is also important. To decrease the intensity of artificial light you could decrease the amount of light, change the Wattage of a bulb, or move the light further back.  Turning the lights off when an area is not in use also helps control light.  On outdoor collections, perhaps you place objects under outdoor enclosures with roofs or on the north side of buildings.

Remember, light damage is permanent and cumulative. No object can be recovered from light damage. Resting objects from the effects of light does not mean that next time they go on dispay that they will be able to handle more light; the object will not “heal”. However, determining how long you would like them to be on display for and knowing the conditions which they are under can help make you decide what is acceptable fading. Objects do have different sensitivities to fading, being aware of this and then deal with those objects accordingly will help reduce the impact that light has upon them. 

Want to have some fun looking at how light damages colours? CCI has a Light Damage Calculator where you can see the how light fades colours under various conditions.  Go to http://www.cci-icc.gc.ca/tools-outils/ldc-cdl/index-eng.aspx to check it out! 

There are other aspects also to consider when looking at lighting, like Colour Rendering, which I have not gone over here but are important to be aware of.

Don’t forget! MAS can help you manage the amount of light that gets into your museum! We have UV and visible light monitors (seen to the right) that can help you out! Give me a shout at 306-780-9266 or [email protected] for more information or for any questions.