Night pool - I'm not sure what this is :) Pool night is an event where everyone is invited to play pool (billiards) or to perhaps have a swim together in someone's pool. Pool night-lights are lights put around a small body of water (a pool of water) to illuminate it at night

Do you mean lights used to illuminate a swimming pool? If so, pool night lights. No hyphen between pool and nights. If you are going to use a hyphen, it should be pool night-lights.