ThinkLight
The ThinkLight is a little LED light integrated into the top edge of the display frame in the A, R, T and X ThinkPad models. It illuminates the ThinkPad's keyboard so that one can type in the dark without using an external light source. The ThinkLight can be controlled via the Fn-PageUp key combination or via ACPI on some of the newer models.
Note that the ThinkLight is not available on the G series ThinkPads.
Linux Support
Controlling the ThinkLight with the keyboard works on all systems since it relies on the BIOS exclusively. Just press Fn-PageUp to toggle its state between on and off.
Support for controlling the light with ACPI is provided by ibm-acpi. After installing it, a simple
echo on > /proc/acpi/ibm/light
switches it on and a
echo off > /proc/acpi/ibm/light
switches it off again.
This allows one to control the light in scripts. Unfortunately, no known ThinkPad comes with a light sensor (yet). ;)
