Now as I understand it, in a typical O'Niel design one end of a colony cylinder end would face the sun and light would be reflected through huge windows with large mirrors. This prevents anyone from having to move their book in a circle to read it. It seems to me all that window area is going to waste and that with artificial lighting the entire interior area of the colony could be used for habitation. A diamond window at the end of the cylinder facing the sun could let light in from the side and the inconvenience of this sideways light could be reduced by having the ground slope up to the far end of the cylinder so everything won't be in shadow. Mirrors and piped sunlight could overcome the problem of sideways light, but artificial lighting might still be easier.