I have noticed that after I set the brightness (High to Low) in Ubuntu 13.10 and then after when I do my work. After rebooting up the PC, the brightness again turns to High. I'm literally tired of this. :'( :(
you should have a look at this thread:
i used the following in a startup script, but that's on an imac: echo 8 > /sys/class/backlight/acpi_video0/brightness
again, have a look at the thread above. lots of advice, something should work for you.