Carolyn Kizer's poem, "Night Sounds" takes place at night when the subject of the poem is trying to sleep. This is the setting.
There is darkness and moonlight (prevalent imagery), which bring about her recollections of time she spent with her husband or lover. The poem speaks to what was and what is. The relationship is over, and though the setting—her bedroom—is the same, and the darkness and moonlight are still there, what has changed—besides noises she now hears that she did not before—is his presence. Awake in her bed, the speaker is able to look more honestly at her time with her departed lover. She recalls that even when they were together, there was a distance that separated them emotionally—a wall he had built. Now that he is gone, the distance is not only emotional, but also physical, supported (again) by the isolation of the night.
The setting of darkness seems to reflect the speaker's emotional state. There is a coldness in the moonlight; aloneness surrounds her; her bed is empty, "no heavy, impassive back to nudge with one foot." She can hear a dog's "hollow cadence" traveling through the night which adds to her sense of emptiness. In her isolation, she faces a night "tinged by terror or nostalgia."
The setting of darkness in the night supports the theme of loneliness experienced by the poem's speaker.