Find the connected minitor name using xrandr (i.e,VGA1)
Then set brightness from 0.1 to 1.0
$ xrandr
$ xrandr --output VGA1 --brightness 0.7
For autostart
$ gnome-session-properties
[Add StartupProgram]
Name --- Brightness-Control
Command --- xrandr --output VGA1 --brightness 0.7
Comment --- Reduce-Screen-Brightness
[Add]
This will create a File named xrandr.desktop in ~/.config/autostart/ Directory
Reboot the system and check
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OR
$sudo gedit /etc/rc.local
# Add this before the last line “exit 0″:
echo 4 > /sys/class/backlight/acpi_video0/brightness
# reboot.
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OR
# gedit /etc/default/grub
#You will find this line in the new opened window:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
#Change it to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
Save and close the window and type this in the terminal:
#
#update-grub
# reboot