Because of the importance of the 18 hour interiors only daylight is used, no shutters. R. H. is maintained at 55-65% through thermal inertia of building plus minimal heating. All paintings are backed with sheets of expanded polystyrene 15 mm thick to isolate them from walls and minimize the risk of the formation of damaging microclimates between the paintings and the walls. Diffuse natural side-light has aesthetic advantages over diffuse top light. -- AATA