If you create Scheduler Task to reset your brightness to 100% at logon using the command below, this does work, but I have found that the brightness dims again somewhere between 10-15 minutes, so I have set the task to run every 10 minutes. Seems to be working.
C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe "(Get-WmiObject -Namespace root/WMI -Class WmiMonitorBrightnessMethods).WmiSetBrightness(1,100)"