Comment 31 for bug 451282

Marten, you might want to try something like this in your /etc/rc.local:

brt=`cat /sys/devices/virtual/backlight/mbp_backlight/brightness`
abrt=`cat /sys/devices/virtual/backlight/mbp_backlight/actual_brightness`
logger -t rc.local "brightness was $brt , actual_brightness was $abrt"
if [ "$brt" != "$abrt" ] ; then
echo $abrt > /sys/devices/virtual/backlight/mbp_backlight/brightness
afterbrt=`cat /sys/devices/virtual/backlight/mbp_backlight/brightness`
logger -t rc.local "changed brightness to $afterbrt and actual_brightness is $abrt"
else
afterbrt=`cat /sys/devices/virtual/backlight/mbp_backlight/brightness`
logger -t rc.local "no brightness change needed, brightness is $afterbrt and actual is $abrt"
fi

This should give you a log entry in /var/log/messages that will show some helpful information when /etc/rc.local executes. So, after booting, check the log with:

$ grep bright /var/log/messages

and see what happened during boot.

It seems like you could have a different problem since your /sys/ entry is different than ours. Take a look in /proc/ to see if you have any more places where brightness is set or shown:

find /proc/ -iname '*bright*'

hth