Can I control brightness on second monitor?

You can do this from the command line (and thus do it automatically each evening via cron) using xrandr as described at How to change LCD brightness from command line (or via script)?

E.g.

xrandr --output HDMI1 --brightness 0.5

This doesn't change the backlight or affect power usage, it just adjusts the gamma value in software. I've heard that Brightness Controller uses xrandr under its GUI skin.

Use xrandr --listactivemonitors to get the correct monitor if not you'll probably get xrandr: Need crtc to set gamma on..

ddccontrol was in Lucid 10.04 and seems to have worked well, but was orphaned by Debian due to lack of interest and hasn't been picked up by anyone since.

Update ddccontrol is back in xenial. See

• #483479 - O: ddccontrol -- a program to control monitor parameters - Debian Bug report logs
• http://packages.ubuntu.com/search?keywords=ddccontrol
• Control external monitor brightness via software
• How to change external monitor brightness via DDC/IC?

Install Brightness Controller from the following PPA.

sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
sudo apt install brightness-controller

Now you can adjust the brightness using the slider.

ADditional info: I'm using CRT monitor. – Neilvert Noval Mar 11 '11 at 17:06It seems that it is not possible to control external monitors using the /sys/class/backlight. But there exists an application called ddccontrol which can control the brightness of your external monitor.

Instructions on how to use the command line interface are available here.

Basically you need to probe for available monitors and controls using ddccontrol -p and look for the address of the control you want in the output and then set the value using ddccontrol -p -r 0x10 -w 70.

Here is the latest information for the brightness controller. There are 2 versions available. Version 1 aka simple version allows support for up to 4 monitors and maintains the classic sliders. Version 2 allows for more specialized control as well as multiple monitors.

You can check them both out here Brightness Controller

For faster install use the PPA

sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt-get update

Then for Version 1

sudo apt-get install brightness-controller-simple

Or for Version 2

sudo apt-get install brightness-controller

Enjoy!

Using xrandr and few lines of bash script, it is possible to control multiple/all monitors at once for convenience

( I use it for 3 monitors + notebook screen at once )

#!/bin/bash
# brightness.sh - script to set multiple monitor brightness
# Author: Nariman Huseynov

# set brightness level from user input & reset if no args provided
if [ -z "$1" ]
then
  echo 'Default brightness 100%'
  LEVEL=1
else
  echo "Setting brightness level to" $1
  LEVEL=$1
fi

# get list of screens,trim noise and remove first line (count)
MONITORS=$(xrandr --listactivemonitors | tail -n +2 | awk '{print $NF}');

# change brightness level per monitor at a time
for each in $MONITORS; do xrandr --output $each --brightness $LEVEL; done

For permanent use:

• add permission to execute:

  $ chmod +x brightness.sh

• move to bin directory (/usr/local/bin in my case)

  $ sudo mv brightness.sh /usr/local/bin/brightness

• execute to set brightness level 50% (night mode)

  $ brightness 0.5

• to reset to 100% brightness

  $ brightness

PS if you don't want error checking and want just few lines, shorter version will do:

# get list of screens,trim noise and remove first line (count)
MONITORS=$(xrandr --listactivemonitors | tail -n +2 | awk '{print $NF}');

# change brightness level per monitor at a time
for each in $MONITORS; do xrandr --output $each --brightness $LEVEL; done

I suggest to use a simple bash script to adjust the brighness of you monitor up or down a single step

Copy bash script below to a file (the name is not important, as long as the name is not similar to other terminal commends). I call it brightness_ext

Then mark it executable with chmod a+x brightness_ext

Bash script

#!/bin/bash

MON="DP-1-1"    # Discover monitor name with: xrandr | grep " connected"
STEP=5          # Step Up/Down brightnes by: 5 = ".05", 10 = ".10", etc.

CurrBright=$( xrandr --verbose --current | grep ^"$MON" -A5 | tail -n1 )
CurrBright="${CurrBright##* }"  # Get brightness level with decimal place

Left=${CurrBright%%"."*}        # Extract left of decimal point
Right=${CurrBright#*"."}        # Extract right of decimal point

MathBright="0"
[[ "$Left" != 0 ]] && MathBright="$Left"00          # 1.0 becomes "100"
[[ "${#Right}" -eq 1 ]] && Right="$Right"0          # 0.5 becomes "50"
MathBright=$(( MathBright + Right ))
[[ "$Right" == 050 ]] && MathBright=5  # if we wanna decrease below 10%
[[ "$CurrBright" == 0.0 ]] && MathBright=5 # we can't go below 0, cause it is negative then

[[ "$1" == "Up" || "$1" == "+" ]] && MathBright=$(( MathBright + STEP ))
[[ "$1" == "Down" || "$1" == "-" ]] && MathBright=$(( MathBright - STEP ))
[[ "$MathBright" -gt 100  ]] && MathBright=100      # Can't go over 1.00

if [[ "${#MathBright}" -eq 3 ]] ; then
    MathBright="$MathBright"000         # Pad with lots of zeros
    CurrBright="${MathBright:0:1}.${MathBright:1:2}"
else
    MathBright="$MathBright"000         # Pad with lots of zeros
    CurrBright=".${MathBright:0:2}"
    [[ "$MathBright" == 5000 ]] && CurrBright=.05
fi

xrandr --output "$MON" --brightness "$CurrBright"   # Set new brightness

# Display current brightness
printf "Monitor $MON "
echo $( xrandr --verbose --current | grep ^"$MON" -A5 | tail -n1 )

• Change MON="DP-1-1" to your monitor name, ie MON="eDP-1-1"

• Change STEP=5 to your step value, eg STEP=2 is less noticeable

Usage

brightness_ext + to increase brightness; brightness_ext - to decrease, fairly simple

Also i suggest you to create shortcuts for those commands, as they are much more convenient to use. Personally I made brightness shortcuts for my both monitors.