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On my laptop I can adjust the brightness just fine, however I am unable to (or at least unable to find the way to) adjust the brightness on my 2nd display. When I have my dual display connected and I adjust the brightness, it only changes on my laptop's screen.
I have f.lux installed and this is working on both displays.
I'm running on a Asus VivoBook S400CA-UH51 with an Intel HD Graphics 4000 graphics card.
There is no built in application for changing the brightness of an external monitor on elementary.
This is also true of basically all the Linux distros and Desktop Environments I know of.
Well, changing the brightness of an external monitor is not always guaranteed to work the same way. Most external monitors have their own settings manager (built into the monitor). Also, remember, an external monitor could be anything from a TV to a Projector.
Too many variables!
Install Brightness Controller with the following commands:
sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
For Version 1 with up to 4 Monitor Support:
sudo apt-get install brightness-controller-simple
For Version 2 with Multi Monitor Support and other features:
sudo apt install brightness-controller
Note: This does not decrease the intensity of backlight, so won't save your batteries. But you can use this as a last resort to save your eyes.
You may be able to adjust the brightness from the terminal using the xrandr command
start with xrandr --listmonitors to find the ID for your 2nd display (in my case it is HDMI-1)
then you will run something like this
xrandr --output HDMI-1 --brightness 0.4
this sets the brightness to 40%
Not very elegant, but it works for me at least. Hope that helps and good luck! :-)
