After Effects CC Light Swipe - black dots and line on render

CC Light Wipe is a transition effect (as implied by it living under Effect > Transition). The black you're seeing is actually the background color of your composition, because it's punching a hole through the layer the effect has been applied to. If you toggle the visibility of the transparency grid, I'm guessing you'll see that instead of the black. 

The intent is that you'd put another clip/image below this one, because that's what you're transitioning to or from. If you want the center of the effect to be white, for example, simply place a white solid or shape layer beneath your footage layer.