As I implied earlier, I'd ban photography, but not go to great lengths to enforce that against people surreptitiously using non-flash cells and point and shoots. The point is to curtail the exposure of the documents to camera flashes. In any case, if you ban flash, you've effectively banned the cameras of all those people who don't know how to turn the flash off.
Much can be done with exhibit design to curtail unwanted visitor behavior. For example, when I visited the Chinese terra cotta warrior exhibit in London a few years ago, groups of a set number were allowed in at set times. As we were queued waiting, museum staff had ample time to lecture us about the rules. Once inside the exhibit, we found ourselves in a large dark room, directed by design and by narrow walkway to pass through in a snaking single-file line. Any use of flash would have produced a hostile reaction from other visitors, due both to the interruption of traffic flow and to the annoyance of being exposed to a flash in a dark room.
