A somewhat overly technical answer, but you did ask "is it possible..."
Open Terminal and go to /sys/class/backlight
, then into the backlight control's directory (the name varies, acpi_video0
in my laptop), then read the files max_brightness
and actual_brightness
. GNOME limits itself to 5 levels between zero and max, but the actual hardware usually has at least 10 levels. If the max_brightness
file says "10" or more, a finer adjustment will be possible.
$ cd /sys/class/backlight
$ ls
acpi_video0@
$ cd acpi_video0
$ ls
actual_brightness device@ subsystem@
bl_power max_brightness type
brightness power/ uevent
$ cat max_brightness
10
You can write the desired level to a file named brightness
in that directory, but in this example GNOME's own tool is used, which does not require root access.
$ pkexec /usr/sbin/gnome-power-backlight-helper --set-brightness 7
or in more recent versions of GNOME the path changed to:
$ pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --set-brightness 7
As Linker3000 said, there might be a GNOME Panel applet for controlling the brightness. Right-click the top panel and choose "Add".
Thanks! (1) I dont have brightness under /sys/class/. Which directory shall I go? (2) I found /sys/class/backlight/ has similar directories acpi_video0 and acpi_video1, both of which have the same-name files. What do acpi_video0 and acpi_video1 mean respectively? (3) The max_brightness files of both directories have the same value 15. But the brightness applet added to the panel also has much more adjustable levels. How is that possible? – Tim – 2011-08-15T18:14:14.450
@Tim: Sorry, it is
/sys/class/backlight
in fact. The two directories may correspond to different devices; you could compare the content of......./acpi_video0/device/uevent
and the PCI IDs reported bylspci
. – user1686 – 2011-08-15T18:25:47.567@Tim: I recall an old rumor about how GNOME would, instead of changing the backlight, simply make the colors darker... The best way to check it is to simply compare the contents of
actual_brightness
before and after adjustments -- if the applet works, but the numbers stay the same, the applet might be faking it. (Remember to check bothacpi_video*
directories.) – user1686 – 2011-08-15T18:29:07.827Thanks! I compared the content of ......./acpi_video0/device/uevent and the PCI IDs reported by lspci, but don't find anything in common. The former says
MODALIAS=acpi:device:
. – Tim – 2011-08-15T18:31:32.893@Tim: How about acpi_video1? The 'device/uevent' file should have PCI_SLOT_NAME if the control belongs to a PCI device (for example, in my laptop acpi_video0 is tied to the ATI Radeon card). If not, it might be a virtual device or something. But in the end, it doesn't really matter -- just adjust whichever works. – user1686 – 2011-08-15T18:34:11.853
......./acpi_video1/device/uevent and ......./acpi_video0/device/uevent have the same content. – Tim – 2011-08-15T18:39:24.180
Why do you say Gnome limits itself to 5 levels? Can we change that on the gnome level ? – Rémi Benoit – 2014-03-27T08:41:09.980
@Rémi: At the time it was based purely on experiments. (However it turns out I was seeing the double-adjustment bug, where each key press would go 2 levels as both GNOME and the video card driver reacted independently, thus halving the 10 levels my laptop had.) – user1686 – 2014-03-27T08:44:47.070
@grawity Ok, I don't got this bug (checked with acpi_event) but still got only 5 level with a maximum_brightness of 854! Did you stumble upon anything else that would block from using fine steps? – Rémi Benoit – 2014-03-27T10:02:36.863