It is not working anymore.
Manage every display's brightness level easily.
It uses xrand's --brightness option, so it does manage display brightness at a software level.
The good part? It should work everywhere.
--brightness brightness
Multiply the gamma values on the crtc currently attached to the output to specified floating value. Useful for overly bright or overly dim outputs. However, this is a software only modification, if your hardware has support to actually change the brightness, you will probably prefer to use xbacklight.