This is a quick tip for removing white speckled lines around the edges of walls and the ceiling. In the image on the left below, the walls were made of a single face, rather than thick walls, with dimension. Single face walls can work, but they often leak light through the corners where two walls meet especially if any of it is at an angle. If the geometry is rectangular and perpendicular, there is usually not a problem. Fix this problem by stretching out the walls to make them thick, or add additional faces behind them.