Krdytkyu

One more way we have to do this is with another new program named as xbacklight , open your terminal and type this

sudo apt-get install xbacklight

then type this xbacklight -set 50

there 50 stands for brightness range we can get it upto 100 from 0 .

you can also increase and decrease the brightness from present value to specified level.as you mentioned if you want to increase to 10% from current value of brightness then you can give this

xbacklight -inc 10

and to decrease 10% you can give this

xbacklight -dec 10 

Warning: xbacklight only works with Intel, not properly on Radeon and not at all with modesetting driver (source).

Open your terminal and type this

xrandr -q | grep " connected"

it will gives you the output as

LVDS1 connected 1680x1050+0+0 (normal left inverted right x axis y axis) 331mm x 207mm

There LVDS1 Stands for your display. So now you have to do as

xrandr --output LVDS1 --brightness 0.5

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

This doesn't change brightness at a hardware level. From randr manual:

--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.

The following works for me:

echo 400 | sudo tee /sys/class/backlight/intel_backlight/brightness

I guess the maximum possible value is in the /sys/class/backlight/intel_backlight/max_brightness file.

Replace intel_backlight with an asterisk to apply to all backlights.

For Laptops,
sudo setpci -s 00:02.0 F4.B=80

Change 80 by [0-FF] to get lowest-highest brightness.
The value specified is in hex, so 80 will give you a 50% of max brightness.

For Desktops [not tested by me],
xgamma -gamma .75

Try this in terminal:

xrandr --output LVDS1 --brightness 0.9

You can change the last value as you like, eg. 0.2

Make this script:

set-brightness.sh

#!/bin/bash

TARGET="acpi_video0"

cd /sys/class/backlight

MAX="$(cat "${TARGET}/max_brightness")"

# The `/1` at the end forced bc to cast the result 

# to an integer, even if $1 is a float (which it 

# should be)

LOGIC="$(echo "($1 * ${MAX})/1" | bc)"

for i in */; do

    if [[ "${TARGET}/" != "$i" && -e "${i}brightness" ]]; then

        cat "${i}max_brightness" > "${i}brightness"

    fi

done

echo "$LOGIC" > "${TARGET}/brightness"

Run it as root, with any value between 0 and 1.

sudo ./set-brightness.sh 0.5

• If your system doesn't have an /sys/class/backlight/acpi_video0, there should be at least one directory in there, which may be device-specific (I also have a radeon_bl0, for example).


• If you have others, keep in mind their values stack (hence the loop; pushing all the other values to 1.0, then setting the target one to the desired amount).


• While acpi_video0 should always work, it doesn't always have the full range of physical brightnesses available. Try each one, and use the one with the largest gamut as your "TARGET"

KDE 4.12:

qdbus org.kde.Solid.PowerManagement /org/kde/Solid/PowerManagement/Actions/BrightnessControl setBrightness 55

KDE Plasma Version: 5.14.3:

The above code is still valid. It will only work if you are a KDE user. However in that case it will require no additional piece of software. It will have the exact same behavior as when using the "battery and brightness" widget. AFAIK it changes the physical backlight, in contrast with xrandr which does does not.

Beware that the 55 above is not a fraction of 100, the latter being the max brightness.
Instead it is related to max_brightness:

qdbus org.kde.Solid.PowerManagement /org/kde/Solid/PowerManagement/Actions/BrightnessControl brightnessMax

There is also a "silent" version that you might prefer in a script:

qdbus org.kde.Solid.PowerManagement /org/kde/Solid/PowerManagement/Actions/BrightnessControl setBrightnessSilent 2000

Refs: qdbus, solid, brightness

Here's a short line that can help you relax your eyes. Just create a crontaab with the line or make a script

xrandr --output VGA1 --brightness 0.5; sleep 20; xrandr --output VGA1 --brightness 1

As @palacsint said, echo 244 > /sys/class/backlight/intel_backlight/brightness path works for me.

But max and min values are resent in /sys/class/backlight/intel_backlight/max_brightness and /sys/class/backlight/intel_backlight/bl_power files respectively.

Also, the actual brightness that your computer is running now is present in /sys/class/backlight/intel_backlight/actual_brightness

Using the above answers, I created this script (saved in my home directory as brightness.sh) to modify display brightness (as the laptop's keyboard suffered a spilled tea issue and became unusable). Feel free to use it (if you have the designated files...otherwise tinkering to point to your variation of them will be necessary).

#!/bin/bash

function main_menu

{

    sudo clear

    cursetting=$(cat /sys/class/backlight/intel_backlight/brightness)

    maxsetting=$(cat /sys/class/backlight/intel_backlight/max_brightness)

    powersave=$((maxsetting/5))

    conservative=$((powersave*2))

    medium=$((powersave*3))

    performance=$((powersave*4))

    echo ""

    echo "----------------------- Brightness -----------------------"

    echo " 1. Set Display to Minimum (Powersave) brightness setting."

    echo " 2. Set Display to Low (Conservative) brightness setting."

    echo " 3. Set Display to Medium brightness setting."

    echo " 4. Set Display to High (Performance) brightness setting."

    echo " 5. Set Display to Maximum brightness setting."

    echo " 6. Exit."

    echo "----------------------------------------------------------"

    if [ $cursetting -eq $powersave ]; then

     cursetting='Minimum'

    else

     if [ $cursetting -eq $conservative ]; then

      cursetting='Conservative'

     else

      if [ $cursetting -eq $medium ]; then

       cursetting='Medium'

      else

       if [ $cursetting -eq $performance ]; then

        cursetting='Performance'

       else

        if [ $cursetting -eq $maxsetting ]; then

         cursetting='Maximum'

        fi

       fi

      fi

     fi

    fi

    echo "        Current Display Setting - "$cursetting;

    choice=7

    echo ""

    echo -e "Please enter your choice: c"

}



function press_enter

{

    echo ""

    echo -n "Press Enter to continue."

    read

    main_menu

}



main_menu

while [ $choice -eq 7 ]; do

read choice



if [ $choice -eq 1 ]; then

 echo $powersave | sudo tee /sys/class/backlight/intel_backlight/brightness

 main_menu

else

 if [ $choice -eq 2 ]; then

  echo $conservative | sudo tee /sys/class/backlight/intel_backlight/brightness

  main_menu

 else

  if [ $choice -eq 3 ]; then

   echo $medium | sudo tee /sys/class/backlight/intel_backlight/brightness

   main_menu

  else

   if [ $choice -eq 4 ]; then

    echo $performance | sudo tee /sys/class/backlight/intel_backlight/brightness

    main_menu

   else

    if [ $choice -eq 5 ]; then

     echo $maxsetting | sudo tee /sys/class/backlight/intel_backlight/brightness

     main_menu

    else

     if [ $choice -eq 6 ]; then

      exit;

     else

      echo -e "Please enter the NUMBER of your choice: c"

      choice = 7

     fi

    fi

   fi

  fi

 fi

fi

done

ddccontrol is another option for controlling backlighting for external monitors. Here I can set the backlight of my external monitor to 50% of its power with:

ddccontrol -p -r 0x10 -w 50

I looked in possible solutions for this problem to improve the way Redshift handles brightness changes. Through there I found that there is a patchset for the Linux kernel to improve compatibility across devices, so that laptops and external screens could work similarly, through sysfs.

In the meantime, ddccontrol is the only thing that works for me here. As usual, the Arch wiki has good overall documentation on the topic as well.

Interactive ncurses-like UI using xbacklight

A poor man's ncurses. Hit h and it goes down 10%, hit l and it goes up 10%. Then show the current luminosity.

xback() (

  done=false;

  echo "less: h, more: l, quit: q"

  while ! $done; do

    read -rsn1 key

    if [ "$key" = h ]; then

      xbacklight -dec 10

    elif [ "$key" = l ]; then

      xbacklight -inc 10

    elif [ "$key" = q ]; then

      done=true

    fi

    printf "r$(xbacklight -get) "

  done

)

Using DBus with Gnome

Steps in brightness for keyboard contol can be implemented with this method as well.

gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.gnome.SettingsDaemon.Power.Screen.StepUp

gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.gnome.SettingsDaemon.Power.Screen.StepDown

Notes

• 
  No root privileges needed! As the /sys/class/backlight way.


• 
  xbacklight not always work.


• 
  xrandr just do a gamma correction
  


• For KDE check this answer