From AnswerHub: Lighting problem [Mac]
I am currently testing UE4 on a Mac at my college, but there are these strange lines where light is being cast onto surfaces. I'm currently wondering if this is just an issue of the Mac not being powerful enough. If anyone could help with this it would be much appreciated.
Run any project on an ATi 4xx0 GPU under OS X.
Head over to the existing Questions & Answers thread and let us know what's up.