It's a pretty dark and bleak world in which the narrator lives. His street is "blind" and "quiet" with a "brown imperturbable [face]." The home's former tenant, a priest, had died inside, and the garden behind the house had grown "wild." The story is set during winter, when "dusk fell before" dinnertime, and the narrator and his friends would play outside in the "dark muddy lanes" and "dark dripping gardens," near the "dark odorous stables."...
It's a pretty dark and bleak world in which the narrator lives. His street is "blind" and "quiet" with a "brown imperturbable [face]." The home's former tenant, a priest, had died inside, and the garden behind the house had grown "wild." The story is set during winter, when "dusk fell before" dinnertime, and the narrator and his friends would play outside in the "dark muddy lanes" and "dark dripping gardens," near the "dark odorous stables." The repetition of the word "dark" is symbolic; this is a dark time for Ireland: its slums are some of the worst in Europe, political tensions are high, and Nationalists see the advent of WWI as an opportunity to rebel against England while she is otherwise engaged.
However, Mangan's sister is always characterized by light, in comparison to the darkness everywhere else. As she stands in the doorway, looking for her brother, the narrator sees her "figure defined by the light from the half-opened door." Later, when he speaks to her, "The light from the lamp opposite [his] door caught the white curve of her neck, lit up her hair that rested there, and, falling, lit up the hand upon the railing." Now, the repetition of light is symbolic, and she seems to represent something hopeful. Perhaps she is meant to represent the writer's hope that, someday, Ireland will not be the bleak and sad place of the narrator's youth. Therefore, Mangan's sister is Ireland's brighter future.