Hi raspberry PI geeks!

I install Raspbian OS, and connected HDMI monitor to one of micro hdmi ports on raspberry pi 4.

Question - how to change brightness of a screen?

I try xrandr: 1) See 2 hdmi:

pi@raspberrypi:~ $ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 7680 x 7680
HDMI-1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768      60.00* 
   800x600       60.32    56.25  
   848x480       60.00  
   640x480       59.94  
HDMI-2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     60.00*+  60.00    50.00    59.94  
   1680x1050     59.88  
   1400x1050     59.95  
   1600x900      60.00  
   1280x1024     60.02  
   1440x900      59.90  
   1280x800      59.91  
   1152x864      59.97  
   1280x720      60.00    60.00    50.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x576       50.00  
   720x480       60.00    60.00    59.94    59.94  
   640x480       60.00    59.94    59.94  

2) Try:

xrandr --output HDMI-2 --brightness 0.1
xrandr --output HDMI-1 --brightness 0.1

Doesn't work Also I tried xbacklight, but it doesn't see external monitor:

pi@raspberrypi:~ $ xbacklight -get
No outputs have backlight property

Also checked : ls /sys/class/backlight/ , but the folder is empty. Note: I want to change brightness, no matter how - through gui/command line. Is it possible? Thanks!

  • Not all HDMI displays support this, I think. You have to configure them manually. – goldilocks Sep 6 '19 at 13:39
  • @goldilocks ok, so.. how to configure it manually?(without touchibg real buttons on monitor) – Ruslan Korolev Sep 7 '19 at 17:02
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    Manually == touching real buttons on monitor. – goldilocks Sep 7 '19 at 17:22

If your display supports DDC, you could be able to adjust the brightness using corresponding tools such as ddccontrol

/sys/class/backlight/ is typically used with built-in screens, where the actual backlight control mechanism is known.

xrandr/xbacklight are purely software-based and cannot alter the backlight brightness, except for OLED screens where displaying darker colors is the way brightness is controlled, since there's no backlight.

  • Hi, thanks for feedback! It supports it (lg.com/ru/monitors/lg-22EA63V-ips-monitors) – Ruslan Korolev Sep 6 '19 at 18:12
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    But I cannot use it with this tool too [code]pi@raspberrypi:~ $ ddccontrol -p Probing for available monitors Detected monitors : No monitor supporting DDC/CI available. If your graphics card need it, please check all the required kernel modules are loaded (i2c-dev, and your framebuffer driver). [/code] – Ruslan Korolev Sep 6 '19 at 18:13
  • Well, that's your answer then: according to the RPi software, your monitor doesn't support changing brightness via HDMI. – Dmitry Grigoryev Sep 8 '19 at 8:31
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    ok thanks for detailed explanation! – Ruslan Korolev Sep 9 '19 at 7:54

xrandr --output VGA-0 --brightness 0.5

  • 1
    Does this work for HDMI monitors? If not, then you really didn't address the question. – Elliot Alderson Jan 31 at 16:18
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    @ElliotAlderson -- if that is your real name ;) -- yes it does (or should, or could). The output label ("VGA-0") is just a label. That said, there's nothing to indicate that to the OP. Of course, that doesn't matter much since it is clear in the question that the OP already tried this. So a bad answer but not quite that bad... – goldilocks Feb 1 at 19:46

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