Thanks for the inputs. At least the iBooks brightness goes low enough to read comfortably at night, unlike the recently updated @$& Kindle app. The Nook app brightness is independent of the system brightness. Nice reading app.
There's a nice little free app called Dimmer, which can be set to a desired brightness. And it can be added to the Notifications area. Then a simple tap puts the preset brightness back to where you like it when finished reading in iBooks. I have mine set at 35% and using auto-brightness.
(Ain't this just a bright post...)