Comment 3 for bug 308784

Here is acpidump.log that you requested

executing "echo -n 1 > /sys/class/backlight/acpi_video0/brightness" or "echo -n 5 > /sys/class/backlight/acpi_video0/brightness" sets this brightness value to 1 or 5 (from 10 available), but this change does not affect the actual backlight lamp brightness

when I'm trying to change brightness with my Fn+F9/F10 keys, I see the adjustment bar at the bottom of my screen, showing more or less brightness depending on key pressing, and value in "/sys/class/backlight/acpi_video0/brightness" is changing correctly, but no actual effect