Greetings!
I installed a fresh Debian 9 with i3 and now am stuck trying to make screen backlight work.
I can see /sys/class/backlight/intel_backlight and change brightness by writing to the corresponding file.
But the keys don’t work and xbacklight says No outputs have backlight property
Furthermore, creating an xorg.conf entry for the device didn’t solve the issue. I also tried popular kernel parameters with no luck.
Anyone had this issue?
Thanks!
The brightness keys sometimes stop working after resuming from sleep. You can reenable them by unloading und reloading a kernel module:
rmmod topstar_laptop
modprobe topstar_laptop
Cheers
nicole
Brightness keys don’t work at all even upon reboot. Reloading the module didn’t help 
LOL
As a fellow i3 user, let me welcome you to the best window manager on the planet. Now that we’ve got that out of the way: i3 doesn’t work the way you think it does. i3 doesn’t have any built-in support for basic hotkeys like volume or brightness.
That’s right. You have to set all that up yourself. For instance in my i3 config file I have the following two lines:
bindsym XF86MonBrightnessUp exec ~/Scripts/brightness-change.sh 5 # increase screen brightness
bindsym XF86MonBrightnessDown exec ~/Scripts/brightness-change.sh -5 # decrease screen brightness
Those call a script that I wrote which will change the brightness. It really just reads and modifies the values in the files within the same /sys/class/backlight/interl_backlight directory you’ve already discovered.
i3 is for people who want to have total control over their experience. It involves a lot of work. But in the end it is worth it. Good luck!