Attached find an article written specifically for one of the questions
you ask. The light is actually quite low compared to a day on the wall
(in a museum). If you have questions give me a call.
http://www.rlg.org/preserv/diginews/diginews2-5.html#technical
Timothy Vitale
Preservation Associates
831-684-2731 Aptos
440-775-7331 (Oberlin, Ohio: till 4/22)