Medieval evenings were as dark as ours. However, with no electricity and smaller windows, rooms - libraries - will generally have been dark places back then. This is why we frequently encounter candle wax on the pages of medieval books. Looking at such yellow blobs, like the one on this image, it’s not hard to imagine the medieval reader bent over his book, holding a candle. In this case to read a law text and scribble clarifying notes between the lines. A bit of wax to illuminate the law.
Pic (my own): Liverpool University, Sydney Jones Library, MS 4.20 (Italy, 13th century)
Over the past month we have added some 30 digital libraries to the DMMapp (http://bit.ly/1elfw1B). In the Public Library of Bruges is Ms. 251, Speculum doctrinale. In the margins of this manuscript you can find scenes of medieval life, such as this puppet show! (f. 191r)
British Library, Additional 22413, detail of f. 71 (historiated initial-word panel of the story of Ruth with Ruth, Naomi and Boaz and his servants working of the field, at the beginning of the Book of Ruth to be read at Shavuot). Joseph Kara, Festival prayer book for Shavuot (Feast of Weeks) and Sukkot (Feast of the Tabernacles), German rite (aka the ‘Tripartite Mahzor’ ) including biblical readings: The Book of Ruth and the Book of Ecclesiastes with Joseph Kara’s commentary. Germany, S. (area of Lake Constance); ca. 1322