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I have a Thinkpad T420 with Nvidia Quadro NVS4200 running binary 319.12 driver. I am using Ubuntu 12.04 with Cinnamon.

The display works fine, and the brightness up/down controls also work in changing the screen brightness. However, the on-screen brightness indicator is wrong.

Whenever I increase the brightness, the indicator shows a low value, even when the screen is on full brightness (pictured). When I decrease the brightness, no indicator shows up.

A screenshot showing the Cinnamon brightness indicator.

The problem also affects Unity. The backlight indicator never moves beyond this low level, and the indicator only shows when increasing brightness:

Screenshot of Unity with indicator issue.

I think this relates to /sys/class/backlight/.

travis@travis-thinkpad-ubuntu:~$ ls /sys/class/backlight
thinkpad_screen

travis@travis-thinkpad-ubuntu:~$ cd /sys/class/backlight/thinkpad_screen

travis@travis-thinkpad-ubuntu:/sys/class/backlight/thinkpad_screen$ ls
actual_brightness  brightness      power      type
bl_power           max_brightness  subsystem  uevent

In theory, the file actual_brightness should hold the current brightness value of the display, which is supposedly between 1 and 7. However, when I run

cat actual_brightness 

The system always returns 0. Maybe this is what the indicator is reading?

I don't have the usual /sys/class/backlight/acpi_video0/.

Is there a way I can get the screen's real brightness to show up?

  • I suppose that the indicator failure is a matter of Cinnamon desktop and not Ubuntu related. Have you tried with other DE ? – NickTux Jul 6 '13 at 23:07
  • The same problem occurs exactly in Unity as well. I will edit the original post with a Unity screenshot too. – Travis G. Jul 6 '13 at 23:46
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In technical details description of Nvidia Quadro NVS 4200M is written, that it has CUDA-Technology - so you could test if this CUDA-driver is supporting this graphics card better instead ? - you can download CUDA-SDK-1.1-beta for Linux here :

http://www.nvidia.de/object/cuda_1_1_beta.html

I have installed this package for my Geforce GT 540M with CUDA-Technology (Optimus) too and it works here proper. You could follow the steps described like here :

https://askubuntu.com/questions/297030/nvidia-frickle-with-hybrid-chipset-is-now-over-finally

When this works at your machine too, - then you have better results too.

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