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Conservation Notes: The fight against (harmful) light

February 25th, 2013

We’ve all seen the yellowing of old photos and the fading of fabrics near windows in our own homes. The effects of light on works of art in our collection could be just as harmful, but our ever-vigilant conservators aren’t about to let that happen. In this post, conservator Katy Whitman explains why and how we keep different kinds of light in check.


Many patrons ask why it is so dark in some of the galleries at the AGO. Many of the works are sensitive to light and need to be kept at low levels to preserve them.

Light exposure causes chemical changes that physically break down the microscopic structure of organic materials, making them brittle and weak and often leading to visible damage, including color shifts and fading. This can be seen in the image of the edge of the acrylic painting above: the edge of the painting was covered by the frame, and when it was removed we discovered that the paint had faded significantly from purple to pale pink. The effects of light exposure are cumulative and irreversible, which means that there is a limited amount of time that an object can be exhibited before serious photochemical deterioration occurs.

Established recommendations for eliminating harmful radiation (ultraviolet and infrared) in exhibit lighting are widespread within the museum community. Further restrictions for the display of museum material depend on many variables and they differ for each institution and each exhibition. These include:

  • Inherent sensitivity of the material composition of an object
  • Object material condition
  • Level of illumination (lux)
  • The duration of the exhibition

Light can be defined with the electromagnetic spectrum (see diagram below). The shorter the wavelength, the more energetic the light. UV (ultra-violet) light has a shorter wavelength than visible light, and therefore is more damaging to artifacts, and we prevent it from penetrating Gallery spaces with special filters on the windows and light fixtures.

While the gallery takes measures to ensure UV light is blocked, it is important to emphasize that visible light as well as UV can cause photochemical damage and that protection from UV does not eliminate the danger of light damage. That is why some works in the AGO’s collection cannot be on display for long periods of time. Some works are more sensitive than others. For example: a painting made of pigment-based paint is much more stable than a chromogenic photograph and therefore can be on display for much longer.


Curious about Conservation?
If you have a burning question about Conservation, leave a comment below. We’ll do our best to give you an answer in an upcoming Conservation Notes post.


Signature Partner of the AGO’s Conservation Program


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