Ja bedankt Gijsbert, gelukt de helderheid vast te zetten op mijn Acer Aspire 6930 en wel als volgt:
1. Check brightness levels by running this command:
sudo cat /sys/class/backlight/acpi_video0/max_brightness
(my laptop max brightness is 9)
2. Set your screen brightness to minimum and check current level by evoking next command
cat /sys/class/backlight/acpi_video0/brightness
(my laptop min brightness level is 0;)
3. sudo gedit /etc/rc.local and add before exit 0 the following line:
echo 9 > /sys/class/backlight/acpi_video0/brightness
Save and from now on this brightness level (9) will be set every time you start your computer.