After having watched Elfar Adalsteins’s “Summerlight… and Then Comes the Night,” I surfed over to Amazon to check the page count of the Jón Kalman Stefánsson book on which the film is based. With its many characters and generational intersections, I imagined it to be an opus on the scale of Tolstoy’s “Anna Karenina” or Dickens’s “Bleak House.” Instead, the novel comes in at 246 pages. This doesn’t seem plausible, given the encompassing nature of Mr. Adalsteins’s picture.