In the light of the comments that have appeared in this thread concerning the Dark Ages, I have been on the lookout for references to the expression in the secondary sources. The historian John Morris made several perceptive comments on this subject in his 1973 book The Age of Arthur, from which the quotes are taken.

The evidence is difficult, but there is plenty of it and it needs to be studied as a whole
"These centuries have often been termed the 'Dark Ages.' They are not dark for lack of evidence. The quantity of evidence is immense and unusually complex, hard to understand. Therefore it has been neglected, abandoned to a small number of specialists, who have often been obliged to limit their studies to their own particular patch... The historian ... must do his best to bring them together, for the evidence seems obscure only because its modern study is inadequate and fragmented." (Introduction)

The name we call a period affects the way in which we study it
"The term 'Dark Ages' is not the innocent invention of conscientious academics, stumped for want of a better term. It has always been used to impose a viewpoint and to suppress evidence. It once comprehended all the 'Gothic' centuries of European history between the Romans and the Age of Enlightenment, and condemned them as inferior. The invention of the term 'Middle Ages' rescued several centuries from obscurity and contempt; but 'Dark Age' remained the designation of European society between the Romans and the Crusaders until the words Merovingian and Carolingian replaced it. It was thenceforth confined to Britain." (Chapter 25: Arthur and the Future)