Setting a display's backlight brightness to be lower than is possible via the normal brightness controls

By normal brightness controls I mean the accelerators on my laptop's keyboard that seem to integrate with Unity.

In a dark room, my screen is quite bright, even on the lowest setting. Can I override this?

I tried setting it explicitly via both:

sudo echo 500 > /sys/class/backlight/acpi_video0/actual_brightness
sudo echo 500 > /sys/class/backlight/intel_backlight/actual_brightness

But I get a permission denied error.

When at the lower bounds via my keyboard's brighness controls, acpi_video0/actual_brightness is 0, and intel_backlight/actual_brightness is 729. Can I set the latter value to be even lower?

Solution 1:

Your command gives elevated permissions to the echo command (which doesn't need them), but not to the part that redirects the output stream to the root-owned file (which does)

In a terminal, you can either do

echo 7 | sudo tee /sys/class/backlight/acpi_video0/brightness

which gives the elevated permission to the bit that really needs it, or

sudo sh -c "echo 7 > /sys/class/backlight/acpi_video0/brightness"

which runs the whole command in a sudo shell

Solution 2:

I created a slider tool based on the information presented here in the question/answers:

• https://github.com/oblitum/backlight.

It provides an alternative slider to control backlight with finer control.