Comment 53 for bug 413399

I'm having a similar issue, I think. In GDM, the brightness fluxuates between roughly 80-90%, and only stops when I'm fully logged in. Once I'm logged in, the brightness will stay the same (usually very low) and if I attempt to change it, it will fluxuate between values. For example, if I tune the brightness down to around 30%, it will fluxuate between roughly 30-40%, and same goes for every setting. I haven't tried manually setting the brightness levels with a command yet, because I don't know what that command would be.