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.
The problem also affects Unity. The backlight indicator never moves beyond this low level, and the indicator only shows when increasing brightness:
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
The system always returns
0. Maybe this is what the indicator is reading?
I don't have the usual
Is there a way I can get the screen's real brightness to show up?