NBS Board member Joel Orosz writes:

"In response to Doug Owens' question about the effects of direct vs. diffused sunlight, you are right to say that direct sunlight is worse than diffused sunlight, but both are bad for books. Even when diffused, sunlight still contains ultraviolet radiation, which will fade books and jackets. It is insidious, since it happens slowly, but it still happens. The only safe level of sunlight in a room with books is zero. Usually, a curtain is not enough, for the UV radiation leaks around the fabric, and often goes right through it. I have a hurricane shutter over the window in the library, which blocks out all sunlight.

On another front, be careful when you next put a bid on a "Blue Book", because you might get the following item, as recently advertised in a catalogue from Oak Knoll Books:

Heartman, Charles. Idem, Semper. The "Blue Book," A Bibliographical Attempt to Describe the Guide Books to the Houses of Ill-Fame in New Orleans as They were Published. Together with Some Pertinent and Illuminating Remarks Pertaining to the Establishments and Courtesans as Well as Harlotry in General in New Orleans. N.p., n.p. , 1936.

On the plus side, you can always say to your spouse, "but dear, I thought it was a coin book"!