YouTube is bursting at the seams with horror shorts, the vast majority of which traffic in the same old jump scares and photoshopped demon faces. David F. Sandberg’s Lights Out, however, managed to distinguish itself from the lurching masses, brilliantly capitalizing on its limitations to present one indelibly shivery concept: namely, a silhouette that creeps closer whenever the lights go off. The James Wan-produced feature-length expansion can’t match the compressed primal frisson of the original, but it contains more than enough flickeringly lit yelps to justify its existence. How many variations can be successfully run on the same gag? Quite a few, as it turns out.