Albert Bierstadt, Mount Corcoran, c. 1876–77
Corcoran Gallery of Art, Washington, D.C.
It is a huge responsibility for museums to conserve and preserve paintings such as the one below illustrating the exploration of the Western United States in 1876.
How do we protect works of art from light damage? Why no flash photography allowed?
Museums around the world struggle with preserving their collections by hiding them away or displaying them for viewing by the public. Many works are 'rotated' in the galleries, limiting the time of light exposure. Exposure to and duration of natural and artificial light are evaluated in combination with the materials used to create the work. The flash from your camera or cell phone not only distract other museum visitors; they can damage the art. This is because they are super-bright, and even though it is only a quick flash, over time, these repeated little moments have a cumulative effect and can add up to big damage including fading, cracking, flaking, and and effect similar to sunburn, where the image darkens over time.
Why does light make colors fade?
Paint, dye, or pigment that fades is called 'fugitive', meaning it goes away, becomes less brilliant, and can shift to another part of the color spectrum. It is important to understand that light affects pigments by both intensity (how bright the light is measured in footcandles fc, or lux) and duration (how long it is exposed to the light.)
Intensity and Duration
Light has the ability to fade paint colors, pigments, and dyes. Fading is increased as the intensity of the light, Ultra Violet component (UV the wavelengths that cause sunburn), and by duration or the number of hours per day a work of art is exposed to light.
Blue pigments have traditionally been the most vulnerable to fading from light exposure, described as 'fugitive.' With the developments of synthetic dyes, and 'fade resistant' pigments there is now a huge range in fading. Care needs to be taken in conserving all art, since to measure the fading of colored surfaces requires light exposure to prove fading, and then it is too late, since the fading has occurred and the damage has already been done and cannot be reversed.
Paper, textiles, and other materials are also damaged by exposure to light, heat, and moisture. 'Yellowing' of paper over time has been witnessed by most of us. Not only has the original color shifted from white to yellow, the fibers themselves have been weakened. Imagine a flag blowing in the sun and wind day after day, eventually it weakens and shreds. We do not want that to happen to our art.
Glass vs. Acrylic Glass for Hospitality Spaces
"Fine art reproductions and works on paper should be framed with standard glass to protect the piece from dust and damage. Once the piece reaches a certain size (ie 30” x 40”) it’s advantageous to use acrylic glass as it minimizes the chance of glass breakage when shipping in bulk, installing or if someone accidentally comes in contact with the face of the piece. If you are specifying for a hospitality project you should almost always specify either glass or acrylic.
The following are also available but are usually prohibitively expensive for hospitality budgets: Non-reflective glass has a “matte” quality to it, which minimizes glare but doesn’t protect from UV damage. Conservation Clear® glass protects art from fading when exposed to light. Museum glass also has UV protection but adds an anti-glare coating that makes the glass practically invisible — a great choice for bright spaces."
ART 101 - THE ART OF SPECIFYING ART - TOP 5 THINGS EVERY DESIGNER NEEDS TO KNOW ABOUT ART SPECIFICATION - Kevin Barry Fine Art 
Testing for Color Fading
Blue dyed wool has been traditionally used to calibrate the fading strength of various light sources. Developed for testing under sunlight, today's museums and artists need new methods for testing fading.
To understand fading, consider how a similar effect is achieved with our blue jeans when they are faded on purpose to make them look old. Our blue jeans fade because of the abrasion, wear and tear, of usage and washing and drying. 'Stone-washed denim' has been marketed to give a pre-faded appearance. Occasionally you will find a small piece of pumice stone or lava rocks, in the pocket of your new jeans, evidence they have been stone washed.
Light test strips.
Traditionally blue wool test strips are used to test for light fading materials. a series of blue dyed strips are placed inside a museum exhibit case with a light blocking strip covering a part of the strip. On a pre-determined schedule, new portions of the strips are exposed to light. This results in a graduated color faded sample, allowing museum conservators to evaluate both the damage done by light sources and the stability of the dyes or pigments.
Test strip from the Northeast Document Conservation Center.
Museum Lighting Research - The Getty