How to change LCD brightness from command line Debian Ubuntu Mint Linux

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To change LCD brightness from command line:

Open your terminal and type this

xrandr -q | grep " connected"

it will gives you the output as eDP-1  connected 1680×1050+0+0 (normal left inverted right x axis y axis) 331mm x 207mm

There eDP-1  Stands for your display .

so now you have to do as

xrandr --output eDP-1 --brightness 0.5

there 0.5 stands for brightness and it ranges from 0.0 to 1.0 . 0.0 -> Full black .so you have to choose the required value of brightness .

from http://askubuntu.com/questions/149054/how-to-change-lcd-brightness-from-command-line-or-via-script