Oddly, there is a control for the keyboard brightness in Power, but nowhere is there a way to adjust my brightness settings for my 2 27" Thunderbolt Monitors. Not even my keyboard button has any effect.
Please post your system info as outlined here:
Also please post the output of the following:
< result > in the next command with the output of the previous command:
ls /sys/class/backlight/< result >
Before I do that, I noticed that in laptop mode, the brightness adjustments work fine and the slider is there in the power section. It’s just not working in clamshell mode. I have an early 2013 MB Pro Retina, 15" 2.7Ghz i7 with 16GB RAM and 1TB SSD. Additionally, if I open the laptop and have a third screen the screen brightness can be changed, but only on the laptop screen not on the 2 thunderbolt monitors.
In regards to your outputs, they are the following:
actual_brightness brightness max_brightness scale type
bl_power device power subsystem uevent
I would just try adjusting the brightness from the buttons of the monitor(s). The brightness buttons don’t work on my windows laptop. So I would only think how less support they would have on a linux laptop.
Additionally, I wouldn’t use a thunderbolt for monitor(s). But the built-in HDMI cables on laptop(s). They prove better performance and compatibility for monitor(s) as compared to thunderbolt(s).
I’m on a MacBook Pro, thunderbolt is my only option. There are no buttons to adjust the brightness.