An superficially neat concept-horror based on a film-short but stretched out to a full movie, and unfortunately the stretch-marks show. It's not a bad film by any means, but it doesn't do enough with it's central idea and it's originality falters in the final act; becoming another traditional ghoul-in-a-house confrontation.
That said, when it works, it works well. A creepy and macabre backstory for the entity ties in with the family drama; and director David F Sandberg provides some effective jump scares and early set pieces, if failing to maintain a necessary sense of dread throughout the movie. The various appearances of 'Diana'; a malevolent spirit that can only exist in the dark (and whose presence is only visible when silhouetted against natural light) are effectively staged. The acting is of an above average standard, although Maria Bello give the most interesting performance as the mentally damaged mother, Sophie. Teresa Palmer and child actor Gabriel Bateman give solid, if forgettable, performances as Sophie's troubled children (from different marriages) while Alexander DiPersia plays the dependable, if slightly undervalued boyfriend. Yet none of them do enough to make you genuinely care. Teresa Palmer's Rebecca is initially shown as some kind of promiscuous wild-child, but the film seems to abandon this line of personality, and it rings false; especially after we learn that she too has undergone the same past trauma as her mother. One could argue that the film is a study of mental illness and its destructive effects on family, but if true, the abrupt conclusion to one character's story arc sends a rather bleak message. In any event, Shutter Island covered that in a far more powerful way.
It also failed my personal bench test: I got home after seeing it (alone) and wasn't thinking about the film or feeling afraid. As someone who can scare easily with supernatural horror, that's not a ringing endorsement. It also seems to break its own rules especially in relation to the effects of light on the entity; one moment it causes it to vanish entirely, but later on in the film its interactions become more physical.
So despite it's promise there is nothing here to elevate Lights Out above the more average horror efforts we're used to seeing. I actually preferred It Follows for its 'quirky concept' innovation; and it's certainly bettered by the likes of The Babadook for substantial scares.