Recently, I felt the need to reduce the brightness of my monitor but did not persuade the hardware buttons to do the job so I started wondering about other means and found that the xrandr command did the trick. The first step was to find out what my display was being called so I executed the following command to retrieve the information using the -q query switch:
xrandr -q | grep " connected"
The output from this looked like this:
DVI-D-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 521mm x 293mm
My device name appeared as the first block of characters in the above so I plugged that into the second command below to achieve the desired adjustment.
xrandr --output DVI-D-0 --brightness 0.9
Any value between 0.0 and 1.0 is acceptable but I went with 0.9 for 90% brightness. The required dimming and brightening then is only a command away.