What:		/sys/class/backlight/<backlight>/bl_power
Date:		April 2005
KernelVersion:	2.6.12
Contact:	Richard Purdie <rpurdie@rpsys.net>
Description:
		Control BACKLIGHT power, values are compatible with
		FB_BLANK_* from fb.h

		 - 0 (FB_BLANK_UNBLANK)   : power on.
		 - 4 (FB_BLANK_POWERDOWN) : power off
Users:		HAL

What:		/sys/class/backlight/<backlight>/brightness
Date:		April 2005
KernelVersion:	2.6.12
Contact:	Richard Purdie <rpurdie@rpsys.net>
Description:
		Control the brightness for this <backlight>. Values
		are between 0 and max_brightness. This file will also
		show the brightness level stored in the driver, which
		may not be the actual brightness (see actual_brightness).
Users:		HAL

What:		/sys/class/backlight/<backlight>/actual_brightness
Date:		March 2006
KernelVersion:	2.6.17
Contact:	Richard Purdie <rpurdie@rpsys.net>
Description:
		Show the actual brightness by querying the hardware. Due
		to implementation differences in hardware this may not
		match the value in 'brightness'. For example some hardware
		may treat blanking differently or have custom power saving
		features. Userspace should generally use the values in
		'brightness' to make decisions.
Users:		HAL

What:		/sys/class/backlight/<backlight>/max_brightness
Date:		April 2005
KernelVersion:	2.6.12
Contact:	Richard Purdie <rpurdie@rpsys.net>
Description:
		Maximum brightness for <backlight>.
Users:		HAL

What:		/sys/class/backlight/<backlight>/type
Date:		September 2010
KernelVersion:	2.6.37
Contact:	Matthew Garrett <mjg@redhat.com>
Description:
		The type of interface controlled by <backlight>.
		"firmware": The driver uses a standard firmware interface
		"platform": The driver uses a platform-specific interface
		"raw": The driver controls hardware registers directly

		In the general case, when multiple backlight
		interfaces are available for a single device, firmware
		control should be preferred to platform control should
		be preferred to raw control. Using a firmware
		interface reduces the probability of confusion with
		the hardware and the OS independently updating the
		backlight state. Platform interfaces are mostly a
		holdover from pre-standardisation of firmware
		interfaces.