The keyboard shortcuts Fn-F5 and Fn-F6 don't change the screen brightness. 
The OSD shows the brightness being altered, but the screen stays at full
brightness.

Extract of dmesg:
[    9.778444] sony_laptop: Sony Notebook Control Driver v0.6
[    9.778581] input: Sony Vaio Keys as
/devices/LNXSYSTM:00/device:00/PNP0A08:00/device:02/SNY5001:00/input/input4
[    9.778644] input: Sony Vaio Jogdial as
/devices/LNXSYSTM:00/device:00/PNP0A08:00/device:02/SNY5001:00/input/input5

[    9.819901] sony_laptop: brightness ignored, must be controlled by ACPI
video driver

Output of spicctrl -a:
/dev/sonypi: No such file or directory

in /dev/sonypi there is a 0 length file available

output of uname -a
Linux 3.11.10-21-desktop #1 SMP PREEMPT Mon Jul 21 15:28:46 UTC 2014 (9a9565d)
x86_64 x86_64 x86_64 GNU/Linux