Laptop backlight brightness increases/decreases 2 steps each time

[Mark]

Hi,

I have a Lenovo 3000 N200 laptop which uses a Nvidia Geforce Go 7300 graphics chip.

I noticed this issue in Lubuntu 11.10 with the Nvidia binary driver and also after booting a Xubuntu 12.04 CD (using the Nouveau driver there I think). As far as I can remember, this issue wasn't present with either Ubuntu 8.04 or Xubuntu 9.10.

The laptop has 8 possible backlight brightness settings. At the desktop, increasing or decreasing brightness (by pressing Fn-F10 or Fn-F11) causes the brightness to increase or decrease by 2 steps instead of 1. However, in text mode -- after switching with Ctrl-Alt-F1 -- changing brightness works as it should, in single steps.

I noticed that the page http://forum.notebookreview.com/acer/434638-linux-acer-1410-1810tz-1810t.html mentions a fix for a similar issue with Acer laptops. That fix adds a line to /etc/rc.local:
  echo N > /sys/module/video/parameters/brightness_switch_enabled

Applying that to my laptop fixed the screen brightness double-stepping at the desktop, so now changing brightness works as it should. However after doing that, the brightness cannot be changed at all when in text mode.

[Ubuntu Foundations Team Bug Bot (crichton)]

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[kotique (kotique)]

Same here. How do we change the stepping of screen brighteness thingie in X11?
Text mode goes correctly from 0 to 8 here, but gnome changes it steps of 2.

Thanks.

[Mark (mark-k)]

Try adding the line shown above to /etc/rc.local, that fixed the brightness changes in X11 for me. Now it moves 1 step at a time in X11, however the brightness cannot be changed at all when not in X11! (That is, in text mode pressing the brightness up/down key has no effect.)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Florian Stoll (flostoll)]

Same problem on Ubuntu 12.04 (3.2.0-26-generic) and Thinkpad T500

echo 0 | sudo tee /sys/module/video/parameters/brightness_switch_enabled

or

echo 4 > /proc/acpi/ibm/cmos
echo 5 > /proc/acpi/ibm/cmos

works -> ~9 brightness steps instead of ~5 steps

dmesg: thinkpad_acpi: detected a 8-level brightness capable ThinkPad

[aka (vangop)]

It seems that echo N > /sys/module/video/parameters/brightness_switch_enabled does help when decreasing the brightness, but when you increase it still goes up in 2 step.
Still, waiting for the fix.

[Florian Stoll (flostoll)]

After installing 3.5.0-18-generic in Ubuntu 12.04 Precise from official repository it seems to be fixed on my Thinkpad T500.

[tanhnhi (tanhnhi)]

Same issue on my Thinkpad X201 (Ubuntu 13.04 64bits). I also noticed that if I click on an entry of the menu bar of any application (for example File menu of Firefox), then use the function buttons to increase/decrease brigthness :
1. Brigthness is increased/decreased in single steps.
2. The Brigthness indicator is not shown.

[Joonas Saarinen (jza)]

This issue is still present in Saucy. I have seen it happen with many laptops, including the HP Compaq 6910p laptop on which I am typing this. It spans across multiple Ubuntu releases. My deduction is that the brightness events are processed by two different recipients which creates the problem. The aforementioned brightness_switch_enabled=N setting seems to mute one of the receivers and thus serves as a functional temporary workaround for many computers.