Comment 2 for bug 423296

Have you tried the following?

1. Add "options thinkpad_acpi brightness_enable=1" to /etc/modprobe.d/acpi-video.conf
2. Update the initrd "sudo update-initramfs -u"
3. Add "acpi_backlight=vendor" to the kernel commandline (in /boot/grub/menu.lst)

But regardless of this, could you please attach the output of "sudo acpidump -o acpidump.txt" to this bug with a short comment to which Thinkpad it belongs. Thanks.