Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
The issue is the color mode the device is set to.. Its probably on auto.
So change the color mode to day , and y ou should be able to go 100% on brightness.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied. If you do not submit a rating, I am in no way credited for my time. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.