Lubuntu brightness/backlight issue

The simplest way I have discovered that doesn't require sudo is to use pkexec lxqt-backlight_backend --inc to increase the backlight brightness and pkexec lxqt-backlight_backend --dec to decrease it.

You can add keyboard shortcuts for these commands in LXQt. I hope this will be fixed soon and it will become the default action for brightness adjustement keyboard combinations instead of the rather useless contrast regulation.

I had the same issue in Lubuntu 20.04. Solution:

1. In terminal run: lxqt-config-globalkeyshortcuts and change:
   lxqt-config-brightness -d => lxqt-backlight_backend --dec
lxqt-config-brightness -i => lxqt-backlight_backend --inc
2. In terminal run: sudo chmod u+s /usr/bin/lxqt-backlight_backend to resolve root permission problem.

You can add the command lxqt-backlight_backend --dec to the 'shortcut config menu' to decrease the brightness and the command lxqt-backlight_backend --inc to increase it.

However, the commands need root permissions to run. One way to overcome this is to manually change the permissions of /sys/class/backlight/intel_backlight/brightness, but the change isn't permanent, since it will be reset after reboot. If I find a way to make the change permanent I will post it here.

I had the same issue for a very long time, but I finally solved it! I was searching for a solution when I found this: https://help.ubuntu.com/community/Lubuntu/Keyboard#Keyboard_shortcuts . And it says:

Control+F10

Laptop screen dim

Control+F11

Laptop screen brighten

I was curious about this shortcut key, because I used a different one to change my brightness. And as soon as I tried, an error popped up saying that xbacklight could not be found. This leaded me to the solution of our problem:

First, I installed xbacklight with the command sudo apt-get install xbacklight. Only this should've worked for me, but my xbacklight was always returning the following error when executed through the terminal:

No outputs have backlight property

So I googled it and found a solution: https://askubuntu.com/a/1060843 This answer solved the error for me. With xbacklight working, I just created shortcut keys for the following commands:

To increase brightness (-time 0 is optional, just for it to change instantly):

xbacklight -inc 10 -time 0

To decrease brightness (-time 0 is optional, just for it to change instantly):

xbacklight -dec 10 -time 0

This is incredibly practical as it doesn't require root to work, so it will work as soon as you add these shortcuts and will last forever (no sudo after reboot for it to work again :D ).

To summarize:

1. Install the xbacklight package with:

   sudo apt-get install xbacklight
   

2. Add the following command to your favourite shortcut keys to increase brightness:

   xbacklight -inc 10 -time 0
   

3. Add the following command to your favourite shortcut keys to decrease brightness:

   xbacklight -dec 10 -time 0
   

4. If the commands don't work, this might be the solution: https://askubuntu.com/a/1060843

References:

• https://help.ubuntu.com/community/Lubuntu/Keyboard#Keyboard_shortcuts
• https://elias.praciano.com/2014/07/xbacklight-comando-para-alterar-o-brilho-do-monitor-lcd-no-linux/ (This tutorial isn't in English)
• xbacklight: No outputs have backlight property - No /sys/class/backlight folder