Because i wasn't able to start my display in the desired brightness automatically, i wrote a little script for dimming the display without of need to remember the whole code.
#!/bin/bash
PS3="Display-Menu:"
select lng in Dimm Dimm+ Dimm++ Display_OFF Display_ON Quit
do
case $lng in
"Dimm")
echo 100 > /sys/class/backlight/rpi_backlight/brightness
echo "$lng - Brightness set to 100";;
"Dimm+")
echo 80 > /sys/class/backlight/rpi_backlight/brightness
echo "$lng - Brightness set to 80";;
"Dimm++")
echo 50 > /sys/class/backlight/rpi_backlight/brightness
echo "$lng - Brightness set to 50";;
"Display_OFF")
echo 1 > /sys/class/backlight/rpi_backlight/bl_power
echo "$lng - Backlight on Display is OFF";;
"Display_ON")
echo 0 > /sys/class/backlight/rpi_backlight/bl_power
echo "$lng - Backlight on Display is ON";;
"Quit")
echo "We're done"
break;;
*)
echo "Ooops";;
esac
done