A burned-out lightbulb is a small domestic annoyance, and the speaker treats it that way at first. "That's tough!" is a shrug, and the plan is simple: buy a stronger bulb tomorrow and screw it in. The tone is casual and a little breezy, as if nothing much is at stake.
But the poem slips sideways. "So what's darkness / among four walls" sounds like bravado, a way of saying the dark doesn't matter. Then the last line jumps to something huge and odd: "The whole earth / in the closet next to the icebox." The speaker seems to be shrinking the world down to household size, or maybe imagining it tucked away among everyday clutter. Judging by the title, the speaker may be standing close to the ceiling, reaching for the socket.
The mood is wry and offhand, with a faint loneliness underneath. A dark room becomes a small stage for big thoughts, which the speaker brushes off with a joke and a trip to the store.