xbacklight - adjust backlight brightness using RandR extension
xbacklight [-help] [-display display] [-get] [-set percent] [-inc percent] [-dec percent]
Xbacklight is used to adjust the backlight brightness where supported. It finds all outputs on the X server supporting backlight brightness control and changes them all in the same way.
Print out the current backlight brightness of each output with such a control. The brightness is represented as a percentage of the maximum brightness supported.
Sets each backlight brightness to the specified level.
Increases brightness by the specified amount.
Decreases brightness by the specified amount.
Print out a summary of the usage and exit.
Length of time to spend fading the backlight between old and new value. Default is 200.
Number of steps to take while fading. Default is 20.
Keith Packard, Open Source Technology Center, Intel Corporation.