Light Damage Page 2
When exposed to sunlight, textiles and paper, fade in colour, or turn yellow, and eventually become brittle. A good illustration of this is obtained by placing a newspaper in the rear window of a car for a few weeks. This yellowing effect to the paper caused by exposure to the UV rays in sunlight is alarming.

This explains why reputable museums are quite dim, with limited light on the exhibits. Any window that allows direct sunlight to fall on an artifact of any sort must be curtained at the very least. Many valuable and rare cloth and paper items have been destroyed over the years by negligent storage where they have been exposed to direct sunlight.
To illustrate the damage caused by light exposure, to the right are two sections of a tent that we place outside every summer. The left side is the storage bag and is the original color. The right side, is the tent which has been exposed to only two summers of sunlight. It is easy to see what happens to paintings, photographs, or cloth items of any sort that are exposed day in, and day out, to sunlight.
On a personal note, I have seen numerous antique tunics that have been proudly displayed in store windows or in collection displays right in front of a window with southern exposure. The result: the exposed side of the cloth has been significantly faded making the tunic almost worthless.Most people can pull an on old favorite T-shirt out, and note that sunlight has faded the outside in comparison to the interior. T-Shirts are cheap. Century old helmets and uniforms are not and they deserve better.