Brightness issues

I have this weird brightness problem where I have it at 50% and it would randomly dim and brighten like crazy. I tested at 100% brightness and it also dims and brightens. Obviously, I don't have it on auto brightness but it sure acts like it.

Anyone with the same issue? Is it a defect? I just got the phone today and I'm afraid to exchange it to have the same problem again. I really like this phone. There's always a friggin issue on a new phone. It's ridiculous.