Why was the lamp lit at noon and what does it say about Ellen and Paul’s situation?

Ellen and Paul are living through a massive dust storm. Though it seems like a simple declarative statement of fact, the story's opening line, "A little before noon she lit the lamp," establishes that the natural state of things in Ellen's world is off. Lighting a lamp just before the brightest part of the day, because dust has blocked the sunlight, introduces the dark and desolate circumstances in which the characters live; it also symbolizes how, amid so much obscuring dust, it will be difficult for Ellen and Paul to see clearly.