On this site, a while ago I found an nice script from someone. THIS IS NOT MINE!

I am using it ever since on my netbook, running Xubuntu and it seems to run on anything.

For reasons of not posting a link-only answer, here it is:

#!/usr/bin/env python



from gi.repository import Gtk

import subprocess



class BrightnessScale:

    def __init__(self):

        # get active monitor and current brightness

        self.monitor = self.getActiveMonitor()

        self.currB = self.getCurrentBrightness()



    def initUI(self):

        # initliaze and configure window 

        window = Gtk.Window()

        window.set_title('Brightness Scale')

        window.set_default_size(250, 50)

        window.set_position(Gtk.WindowPosition.CENTER)

        window.set_border_width(10)



        # slider configuration

        self.adjustment = Gtk.Adjustment(self.currB, 0, 100, 1, 10, 0)

        self.scale = Gtk.HScale()

        self.scale.set_adjustment(self.adjustment)

        self.scale.set_digits(0)



        # close Gtk thread on closing window

        window.connect("destroy", lambda w: Gtk.main_quit())



        # setup event handler on value-changed

        self.scale.connect("value-changed", self.scale_moved)



        # add the scale to window

        window.add(self.scale)



        # show all components in window

        window.show_all()



        # close window on pressing escape key

        accGroup = Gtk.AccelGroup()

        key, modifier = Gtk.accelerator_parse('Escape')

        accGroup.connect(key, modifier, Gtk.AccelFlags.VISIBLE, Gtk.main_quit)

        window.add_accel_group(accGroup)



    def showErrDialog(self):

        self.errDialog = Gtk.MessageDialog(None, 

                                           Gtk.DialogFlags.MODAL,

                                           Gtk.MessageType.ERROR,

                                           Gtk.ButtonsType.OK,

                                           "Unable to detect active monitor, run 'xrandr --verbose' on command-line for more info")

        self.errDialog.set_title("brightness control error")

        self.errDialog.run()

        self.errDialog.destroy()



    def initStatus(self):

        if(self.monitor == "" or self.currB == ""):

            return False

        return True



    def getActiveMonitor(self):

        #Find display monitor

        monitor = subprocess.check_output("xrandr -q | grep ' connected' | cut -d ' ' -f1", shell=True)

        if(monitor != ""):

            monitor = monitor.split('

')[0]

        return monitor



    def getCurrentBrightness(self):

        #Find current brightness

        currB = subprocess.check_output("xrandr --verbose | grep -i brightness | cut -f2 -d ' '", shell=True)

        if(currB != ""):

            currB = currB.split('

')[0]

            currB = int(float(currB) * 100)

        else:

            currB = ""

        return currB



    def scale_moved(self, event):

        #Change brightness

        newBrightness = float(self.scale.get_value())/100

        cmd = "xrandr --output %s --brightness %.2f" % (self.monitor, newBrightness)

        cmdStatus = subprocess.check_output(cmd, shell=True)



if __name__ == "__main__":

    # new instance of BrightnessScale

    brcontrol = BrightnessScale()

    if(brcontrol.initStatus()):

        # if everything ok, invoke UI and start Gtk thread loop

        brcontrol.initUI()

        Gtk.main()

    else:

        # show error dialog

        brcontrol.showErrDialog()

How to use

• Paste the script into an empty file, save it as brightness_set in ~/bin (you probably have to create the directory). Make it executable




• Add it to a shortcut key: Choose: System Settings > "Keyboard" > "Shortcuts" > "Custom Shortcuts". Click the "+" and add the command:

  
  
  

  brightness_set
  
  




• Log out and back in and it should work

Edit

To make a nice set, you could make the slider available in Dash, the Launcher or any other application menu, by adding a .desktop file in ~/.local/share/applications

[Desktop Entry]

Type=Application

Name=Brightness Scale

Icon=/path/to/set_brightness.png

Exec=brightness_set

OnlyShowIn=Unity;

• In the Icon= line, set the path to the icon. Yopu can choose your own icon, or save the icon below as set_brightness.png:

  
  
  

  



• In the Exec= line, the assumption is that the script is in $PATH (which includes ~/bin on Ubuntu), and executable