Comment 10 for bug 226503

the solution for editing the proc tree over rc.local might be using the following syntax in the rc.local file:

instead of
echo 1 > /proc/acpi/video/*/DOS
use this syntax:
for f in /proc/acpi/video/*/DOS; do echo 7 > $f; done

i got the solution from here:
http://bbs.archlinux.org/viewtopic.php?id=39840

it works fine for me.