How to change LCD brightness from command line (or via script)?

Question

To work around bug #1005495 (changing LCD brightness via hotkeys impossible), I'd like to have one command line query for increasing and one for reducing the brightness of my LCD. I could then map a hotkey to each one of this queries.

The problem is: I don't know how to increase and reduce the LCD brightness on the command line. Do you?

score 194 · Answer 1 · edited Jan 04 '19 at 22:48

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.

score 175 · Answer 2 · edited Jan 04 '19 at 22:26

175

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.

edited Jan 04 '19 at 22:26

Pablo Bianchi

17,371

answered May 19 '14 at 09:51

palacsint

2,227

score 162 · Answer 3 · edited Jul 13 '20 at 19:25

Note: xbacklight only works with Intel, not properly on Radeon and not at all with modesetting driver (source). It also only works on X11, not Wayland.

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

Pablo Bianchi · Answer 4 · 2024-11-25T23:02:26.390

Using D-Bus with GNOME

You can increase/decrease brightness with gdbus:

# Step up
gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.gnome.SettingsDaemon.Power.Screen.StepUp
Step down
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! Unlike the /sys/class/backlight way.
Source: Arch wiki (here for keyboards).
xbacklight not always work.
xrandr (from x11-xserver-utils) just does a gamma correction.
Probably works on MATE and Xfce. For KDE check this answer, using qdbus.
ddcutil might work on external monitors with DDC support

score 13 · Answer 5 · edited Jun 04 '19 at 22:44

13

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 to make a gamma correction (not tested by me),

xgamma -gamma .75

edited Jun 04 '19 at 22:44

Pablo Bianchi

17,371

answered Jun 10 '12 at 17:37

Gaurav Gandhi

1,680

score 7 · Answer 6 · edited Mar 09 '16 at 19:30

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"

int_ua · Answer 7 · 2018-12-21T09:41:01.727

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

score 3 · Answer 8 · answered Oct 12 '19 at 02:08

To set absolute brightness (for laptop users):

BRIGHTNESS=50 # 0 to 100

dbus-send \
--session \
--type=method_call \
--dest="org.gnome.SettingsDaemon.Power" \
/org/gnome/SettingsDaemon/Power \
org.freedesktop.DBus.Properties.Set \
string:"org.gnome.SettingsDaemon.Power.Screen" \
string:"Brightness" \
variant:int32:$BRIGHTNESS

score 3 · Answer 9 · edited Jul 14 '25 at 19:24

brightnessctl

I am using i3 as my window manager and I had uninstalled gnome, so the gnome solution didn't work for me. And the other software based approaches just made the screen look more black. So, after a bit of reading, I came across brightctl.

sudo apt install brightctl

You will need permissions to modify the display device, which only members of the group video (and obviously root) can do. So, make sure you add the current user to the video group. You can do this like so:

sudo usermod $(whoami) -a -G video
# or
sudo adduser $USER video

After installation, I can increase/decrease brightness using the below commands by 10. This is very gradual and gives me more control:

# Increase brightness
/usr/bin/brightnessctl -d intel_backlight set +10
Reduce brightness
/usr/bin/brightnessctl -d intel_backlight set 10-

I have added key bindings in my i3 config. Here is a snippet of the key binding.

# Increase brightness
bindsym XF86MonBrightnessUp exec /usr/bin/brightnessctl -d intel_backlight set +10
Reduce brightness
bindsym XF86MonBrightnessDown exec /usr/bin/brightnessctl -d intel_backlight set 10-

score 3 · Answer 10 · edited Sep 22 '13 at 22:47

3

Try this in terminal:

xrandr --output LVDS1 --brightness 0.9

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

edited Sep 22 '13 at 22:47

Eric Carvalho

55,453

answered Sep 22 '13 at 22:12

score 3 · Answer 11 · answered Mar 07 '14 at 20:32

3

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

answered Mar 07 '14 at 20:32

Cristianpark

47

score 3 · Answer 12 · answered Dec 07 '14 at 05:59

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

score 3 · Answer 13 · edited Apr 20 '21 at 20:15

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=$((maxsetting/5))
  conservative=$((powersave2))
  medium=$((powersave3))
  performance=$((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

score 3 · Answer 14 · answered Jan 25 '18 at 22:14

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.

score 2 · Answer 15 · answered May 21 '21 at 00:45

To increase brightness using xdotool, run the following command:

$ xdotool key XF86MonBrightnessUp

To decrease brightness using xdotool, run the following command:

$ xdotool key XF86MonBrightnessDown

Since xdotool simulates real hardware keypresses, this is a hardware level change of brightness.

Source: https://linuxhint.com/display_brightness_commandline/

score 2 · Answer 16 · answered Nov 15 '17 at 21:40

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
)

score 0 · Answer 17 · answered Mar 11 '20 at 10:36

0

Based on placsint's answer

cd /sys/class/backlight/intel_backlight/
cat max_brightness | sudo tee brightness

answered Mar 11 '20 at 10:36

Rolf

2,229

Alfred.37 · Answer 18 · 2022-09-30T18:35:06.710

0

You can set the x% brightness of display on follow way:

Syntax:

sudo brightnessctl -d intel_backlight set [your wanted value in % of max]

Install brightctl:

sudo apt install brightctl

Set the brightness to one % value in a range of 0 - 100 %:

sudo brightnessctl -d intel_backlight set 60%

edited Sep 30 '22 at 18:35

answered Sep 30 '22 at 18:07

Alfred.37

159

How to change LCD brightness from command line (or via script)?

18 Answers18

Using D-Bus with GNOME

Step down

Notes

KDE 4.12:

KDE Plasma Version: 5.14.3:

brightnessctl

Reduce brightness

Reduce brightness

Linked

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