cat /var/log/upstart/brightness-*.log:

Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 10
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802
Using saved value: 21802

 -l /sys/class/backlight

 lrwxrwxrwx 1 root root 0 mar 22 23:03 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
 lrwxrwxrwx 1 root root 0 mar 22 23:03 intel_backlight -> ../../devices/pci0000:

cat /sys/class/backlight/*/brightness

10
21802

cat /sys/class/backlight/*/max_brighness

10
43605

ls -l /var/lib/backlight

drwxr-xr-x 2 root root 4096 mar 18 17:22 acpi_video0
drwxr-xr-x 2 root root 4096 mar 18 17:22 intel_backlight

cat /var/lib/backlight/*/brightness

10
21802

cat /var/lib/backlight/*/max_brightnes

cat: /var/lib/backlight/*/max_brightnes: No such file or directory