Natural light, incandescent light, florescent light all
damage paper to differing degrees. The damage is cumulative and
non-reversible. Look at a
newspaper that’s been in the sun for even a week – yellow and brittle. Colored
construction paper will bleach in the sun. Not just paper – any textile will lose its color in the sun.
Move furniture off a rug after it’s been there a long time and guess what the
rug underneath has stayed the same color while the part exposed to the light
has bleached. The primary culprit is ultraviolet light (uv rays). Museums deal
with the problem by rotating their exhibits to give an object rest. Current thinking says display should
not exceed three or four months.
Light is carefully controlled in most museums through filters on windows
or florescent lights. Some exhibits are lit only when they are being viewed. The Declaration of Independence
is protected by multiple glass layers which remove not only the uv light but
also other potentially harmful parts of the visible light spectrum. (Visible
light is the spectrum between infrared light and ultraviolet light. It is the light that we can see as the
name implies.)
Museums use light meters to
determine the amount of light that is bombarding an object. Light is measures
in terms of lux or lumen.. (Here
come some definitions. Don’t blame
me this is just how the people in the know think about measuring light. ) First are footcandles. That is pretty obvious. A footcandle is the amount of light or
illumination at one foot from the candle. The actual definition is a little
more complex, but that’s essentially what it means. One footcandle is equal to one lumen per square foot. I told you you would hate this. Lights are usually measured in
lumens. According to Wikipedia a
25 watt compact fluorescent lamp emits about 1,500 to 1,600 lumen (http://en.wikipedia.org/wiki/Lumen_(unit). Obviously the less lumen the
better. Moving on. One footcandle is equal to
approximately 10 lux. It actually
10.765 lux, but who’s being picky.
There are set recommendations of how much lux (light intensity) is
recommended for each type of object.
For example, for textiles the recommended amount is 5 footcandles or 50
lux. For leather, oil painting and
other less light sensitive objects it is 15 footcandles or 150 lux. As I said, you measure the amount of
light with a light meter. There’s
also a gadget that has beads that change color from white to blue when there is
uv light exposure. That's fun!
That’s all well and good, but what
does it mean. For archives and
museums charged with preservation of material it is extremely important. Fragile material must be kept out of
the light as much as possible. Storage areas should
not have outside windows. Even
exhibit space should control natural light. As I said this can be done with uv filters on
windows and on fluorescent lights. Most exhibits have subdued
lighting with a minimum aimed at the object. Objects should be
rotated and rested.
But what can you do at home. Well, there are a number of things.
First being aware of the damage that light can cause will help you choose where
to hang your favorite watercolor or photograph or Declaration of Independence. Reduce the amount of natural light
hitting an object by drawing the shades or drapes during the day. Just reducing the number of light
fixtures in a room or the wattage of bulbs will help. Dimmer switches are one option. Turn out those lights when you leave the room. Saves energy and reduces the electric
bill too. You can’t lose. Change your pictures now and then. For photographs or framed items there
is uv filtered glass that you can use.
It is more expensive, but if you have a treasured item, it can be worth
it.
Here’s a few websites with
additional information.
http://www.pbs.org/wgbh/nova/charters/fading.html - (about the Declaration of Independence)
That’s a very quick overview of light and the damage it can
cause. Next time – temperature and humidity. Whoopee!!!
