They’re similar, but not exactly the same. "It's going to be a late night." Focuses on time — you’ll be awake or busy until late, probably past your usual bedtime. Common in contexts like work, studying, or going out. Examples: I have so much homework. It’s going to be a late night. We’re going to a concert, so it’ll be a late night. "It's going to be a long night." Focuses on duration and often difficulty or intensity — the night will feel long, possibly because of stress, work, or emotional effort. Can be positive or negative, depending on tone. Examples: The baby won’t stop crying. It’s going to be a long night. We’re pulling an all-nighter to finish this project. It’s going to be a long night. Summary: Late night = ends late (time-based) Long night = feels long (effort-based)