Scared of the dark? Well, the new "Lights Out" trailer is going to give you nightmares — if you can even go to sleep!

The premise of the horror movie is pretty simple: A monster terrorizes a young woman and her kid brother when the lights are turned off. The monster's name is Diana and was friends with their mother as children. But something terrible happened to Diana, and now she haunts the entire family.

Fear of darkness is something that many people had as kids (or even as adults), and the movie plays brilliantly to that. The few glimpses we get of Diana are creepy, and the family dynamic adds drama to the basic scares.

"Lights Out" stars Maria Bello, Teresa Palmer, Gabriel Bateman, and Charlotta Losten, and opens in theaters July 22.

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