This program is designed for people who like dark screens and want to protect their eyes. So if your monitor is too bright, especially during the night - even if you set the brightness to minimum, download Night Mode for Windows - a small tool to dim your whole desktop and all windows on all monitors.
You may also use global keyboard shortcuts:
CTRL + Windows key + F11 to decrease brightness
CTRL + Windows key + F12 to increase brightness
CTRL + Windows key + F9 to maximum dim...