Several months of exposure to even very low light levels may have the same effects on paper as a few days of direct sunlight. Damage by light is not reversible. Storing book collections and other paper items in the dark may not be practical. Suitable precautions may include storage out of direct sunlight, use of special UV filtering shields on windows and lights, and use of heavy draperies. Valuable papers, such as old deeds, diplomas, etc. can be kept in acid-free file folders in low light areas.
Competent framers can mount and mat valuable documents with acid-free boards.
However, it should not directly touch the paper item framed. A steady RH between 45 to 60 percent is acceptable for papers. Mold growth is likely to occur when the RH level is over 65 percent. Too low an RH level can cause drying out and brittleness. Then expose the paper to an hour of sunlight or UV and circulating air to kill or reduce mold.