I have connected my Acer Chromebook to external screen and keyboard. How can I control the display brightness? (the screen does not have its own controls.) Usually I can click the brightness buttons in the built in keyboard but here I am using an external keyboard and also setting the built-in keyboard brightness only affects the built in screen and not the external one.
--brightness brightness Multiply the gamma values on the crtc currently attached to the output to specified floating value. Useful for overly bright or overly dim outputs.
You would use it like this:
xrandr --output <output> --brightness <brightness>
First, you need to find the name of the output:
There should be several results displayed, with at least two of those marked "connected". My external VGA screen is called "DP1".
For brightness values, "1" is default; "2" is extra bright, "0.5" is dim-ish.
So for me, the command for a little extra brightness looks like this:
xrandr --output DP1 --brightness 1.2