BacklightBrightness

How to change backlight brightness:

An easy way to change backlight brightness is to install Xfce's power manager as follows:

apt install xfce4-power-manager

After installation, Menu --> Applications --> Settengs --> Power Manager --> Launch it
Then, FN + F6 key decrease brightness and FN + F7 key increase it.

As for other ways, see https://sourceforge.net/p/mx-respin-lxde/wiki/BacklightBrightness/