Ghosts can attract, but you can't see it, and it can't see you, because you two have different spatial dimensions. Accurately speaking, you attract not ghosts, but' souls', that is, radio waves, because radio waves fill the whole space, and umbrellas are similar to radio receivers; As for time, because there is no interference from solar waves at night, radio waves are easier to gather; It doesn't matter where it is, playing an umbrella in the house in the middle of the night can attract ghosts.