Decrease Backlight Below Minimum

Solution 1:

1. Open Terminal (Ctrl+Alt+T).

2. Enter the following command:

   cat /sys/class/backlight/intel_backlight/brightness
   

3. Write down the resulting value (12421 in my case).

4. Divide value by 6 and write it down (2070 in my case).

5. Enter the following in the terminal, replacing 2070 with your value:

   sudo su -c "echo 2070 >/sys/class/backlight/intel_backlight/brightness"

6. Close Terminal.

7. For future usage of the last command, open Terminal, press Ctrl and R together, start typing brightness. When the last command appears, just press Enter.

It works for me on a Samsung NC110 with Ubuntu 12.04.

Solution 2:

None of the answers here worked for me (on a Dell Precision 5510). The output from cat /sys/class/backlight/intel_backlight/brightness for me was 1 and setting it any lower completely turned the screen off.

I finally found a solution from the answer here:

xrandr --output eDP1 --brightness .3

I was also able to get this to work on my external monitor (attached via a display port dock), and reduce it below the minimum brightness allowed by the hardware controls on the monitor:

xrandr --output DP1-1 --brightness .6

Note that your display might not be eDP1 (or DP1-1), but you can list all available displays by hitting tab twice after --output, or from xrandr -q which shows which ones are currently connected. Tweak the value for brightness, i.e., .4, .5, etc until you find a level that works for you.

Solution 3:

Try to override the min brightness manually with

1. sudo nano /sys/class/backlight/acpi_video0/brightness

2. Change the value in this file to 0 (clear and type 0 if value is already 0).

3. Press Ctrl + X to exit.

4. Press Y and Enter to save the file.

This works for me. You can also try sudo sh -c 'echo 0 > /sys/class/backlight/acpi_video0/brightness'

I am still looking for a more robust approach. Any help is appreciated.