-The <level> number range is 0 to 7, although not all of them may be
-distinct. The current brightness level is shown in the file.
+Sysfs notes:
+
+The interface is implemented through the backlight sysfs class, which is poorly
+documented at this time.
+
+Locate the thinkpad_screen device under /sys/class/backlight, and inside it
+there will be the following attributes:
+
+ max_brightness:
+ Reads the maximum brightness the hardware can be set to.
+ The minimum is always zero.
+
+ actual_brightness:
+ Reads what brightness the screen is set to at this instant.
+
+ brightness:
+ Writes request the driver to change brightness to the given
+ value. Reads will tell you what brightness the driver is trying
+ to set the display to when "power" is set to zero and the display
+ has not been dimmed by a kernel power management event.
+
+ power:
+ power management mode, where 0 is "display on", and 1 to 3 will
+ dim the display backlight to brightness level 0 because
+ thinkpad-acpi cannot really turn the backlight off. Kernel
+ power management events can temporarily increase the current
+ power management level, i.e. they can dim the display.
+