$ ls /sys/class/backlight

$ ls /sys/class/backlight
intel_backlight

$ ls /sys/class/backlight/intel_backlight
actual_brightness  brightness  max_brightness  subsystem  uevent
bl_power           device      power           type

$ cat /sys/class/backlight/intel_backlight/brightness
                           ^^^^^^^^^^^^^^^
                           自分の環境に合わせる。

echo xxx > /sys/class/backlight/intel_backlight/brightness
                                ^^^^^^^^^^^^^^^
                                自分の環境に合わせる。
"xxx"には覚えたおいた数値を記述します。

$ modinfo sony-laptop
filename:       /lib/modules/3.2.0-32-generic/kernel/drivers/platform/x86/sony-laptop.ko
version:        0.6
license:        GPL
description:    Sony laptop extras driver (SPIC and SNC ACPI device)
author:         Stelian Pop, Mattia Dongili
srcversion:     6C9826483D41F8A630A7AC7
alias:          acpi*:SNY6001:*
alias:          acpi*:SNY5001:*
depends:        
intree:         Y
vermagic:       3.2.0-32-generic SMP mod_unload modversions 
parm:           debug:set this to 1 (and RTFM) if you want to help the development of this driver (int)
parm:           no_spic:set this if you don't want to enable the SPIC device (int)
parm:           compat:set this if you want to enable backward compatibility mode (int)
parm:           mask:set this to the mask of event you want to enable (see doc) (ulong)
parm:           camera:set this to 1 to enable Motion Eye camera controls (only use it if you have a C1VE or C1VN model) (int)
parm:           minor:minor number of the misc device for the SPIC compatibility code, default is -1 (automatic) (int)
parm:           kbd_backlight:set this to 0 to disable keyboard backlight, 1 to enable it (default: 0) (int)
parm:           kbd_backlight_timeout:set this to 0 to set the default 10 seconds timeout, 1 for 30 seconds, 2 for 60 seconds and 3 to disable timeout (default: 0) (int)