Light & Dark

Setting: It's late on a weekday night. Kids are in bed and supposedly asleep. Dad looks upstairs and sees a light on in Max's room.
Dad: "Max?"
Max: "Yeah."
Dad: "Why is your light on?"
Max: "Because it's dark and I need it to see."
Dad: "What are you supposed to be doing?"
Max: "Sleeping."
Dad: "You can't sleep very well with the light on."
Max: "Oh."
Note: The light goes off.