I'm getting very harsh banding from lights on PC not getting same result on a Mac

Hey all, so I teach an AE class and i'm finding that when I use a light with a 3d object I'm getting tons of harsh banding. When I open the same file on a Mac banding is fairly minimal. Any idea why? PC is a big heafty workstation, lots of GPU mem, and processing etc. Mac pro's at school are a few years old. I've tried uping render quality, made color space 32 still no change. Also this is fairley recent, haven't run into this issue in the past.