reduce Screen brightness in battery mode automatically

Question

KDE and XFCE4 has a program to adjust the screen brightness automatically in battery mode to a preset value. How can i set the same with Unity ( or Gnome3 )?

Answer 1

I found the solution:

If you have laptop-mode-tools installed

cat /sys/class/backlight/acpi_video0/brightness
cat /sys/class/backlight/acpi_video0/max_brightness
sudo -H gedit /etc/laptop-mode/conf.d/lcd-brightness.conf

---

Contents should be:

DEBUG=0
CONTROL_BRIGHTNESS=1
BATT_BRIGHTNESS_COMMAND="echo [min value]"
LM_AC_BRIGHTNESS_COMMAND="echo [max value]"
NOLM_AC_BRIGHTNESS_COMMAND="echo [normal value]"
BRIGHTNESS_OUTPUT="/sys/class/thermal/cooling_device0/cur_state"

---

Sources:

• Arch Wiki: laptop-mode-tools
• Gentoo forum

Answer 2

1. Download and install Cuttlefish
   This tool helps in a lot of stimulus based reactions.
2. Install xbacklight
   sudo apt-get install xbacklight
   This tool helps in changing brightness via command line.
   Now make a file(say dim) with following content:
   #!/bin/bash
xbacklight -set 10
   This command reduces your brightness to 10%.
   Change the mode of the file:chmod +x dim
3. Open the Cuttlefish application(using dash) and add a new reaction.Add a new stimulus Power Cable Unplugged from the Hardware category.

Next you need to set up the reaction.Go to Reaction>Applications>Start Application(Advanced Mode)

Now choose the executable as dim(file that we created earlier)

You may also want to increase the brightness when power is plugged again.For that follow the same steps except write xbacklight -set 100 and change stimulus to Power Cable Plugged In.

To make it work, you need to enable cuttlefish to start automatically. Go to edit/preferences (within cuttlefish) and enable start up .