ACPI object of ALS

http://www.freebsd.org/doc/en/books/handbook/acpi-debug.html
http://fred-zone.blogspot.com/2008/10/bios-acpi-description-table.html
http://lwn.net/Articles/348576/
http://www.acpi.info/presentations/ACPI_Overview.pdf
http://acpi.sourceforge.net/dsdt/index.php
http://biosengineer.blogspot.com/2007/10/acpi-table.html
http://zh.wikipedia.org/wiki/ACPI
http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/DirAppLaunch_Vista.doc

acpi_evaluate_object (acpi_handle object, acpi_string pathname, struct acpi_object_list *parameter_objects, struct acpi_buffer *return_object_buffer);

Using acpi_evaluate_object to read/write the acpi objects, to control or get info from BIOS or devices.

9.2 Control Method Ambient Light Sensor Device
9.2.1 Overview
9.2.2 _ALI (Ambient Light Illuminance)
9.2.3 _ALT (Ambient Light Temperature)
9.2.4 _ALC (Ambient Light Color Chromacity)
9.2.5 _ALR (Ambient Light Response)
9.2.6 _ALP (Ambient Light Polling)
9.2.7 Ambient Light Sensor Events
9.2.8 Relationship to Backlight Control Methods