George Henderson is Emeritus Professor of Medieval Art at the University of Cambridge. A specialist on the Insular tradition, his publications include Vision and Image in Early Christian England and From Durrow to Kells (1987).
Librarian Note: There is more than one author in the Goodreads database with this name.
It's an architecture book, so more detail than I wanted on occasion, but nice ties to the social fabric and he agrees that the windows are too dark and it answered all my questions. A quick read, too, compared to Mont St. Michel and Chartres.