I updated my ubuntu to 15:04 , but after que I can no longer reduce brightness. Even when I try with FN keys, the indicator varies, but the brightness doesn't change.
I've tried many ways to change the brightness, but nothing works. Seems like the video drivers doesn't response to command.
It may be helpful:
~$ ls /sys/class/backlight/ intel_backlight
Section "Device" Identifier "card0" Driver "intel" Option "Backlight" "intel_backlight" BusID "PCI:0:2:0" EndSection
About my laptop:
~$ lspci -k | grep -EA2 'VGA|3D' 00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09) Subsystem: Holco Enterprise Co, Ltd/Shuttle Computer Device 2032 Kernel driver in use: i915
Graphics: Intel® Ivybridge Mobile
Model: Positivo Unique S1991i