Adjusting monitor brigthtness level via software


  • Module Developer

    Now that I’ve got my mirror running software-wise and I’m about to make an actual mirror out of it, I was wondering about how to make sure the screen background isn’t visible at night. My monitor supports DDC/CI but from the little information I could gather online, it seems the Pi doesn’t support controlling an external monitor via DDC/CI (yet?).

    There’s ddccontrol, but at least on my Pi 1 it didn’t work when I tried to use it, but I also have no idea what I’m doing, as I’ve only recently started experimenting with my Pi and I’m lacking the background on how a computer communicates with the monitor. It seems that most linux distributions allow for a change of the brightness level via /sys/class/backlight, but the Pi’s backlight folder is empty.

    Ideally I would like to attach a light sensor to my Pi that could automatically reduce screen brightness as soon as it gets dark inside a room, but to have that happen, I would have to find a way to adjust screen brightness using the Pi rather than my monitor’s OSD.

    Any help is appreciated :)


  • Module Developer

    I don’t of anything that directly controls the monitors brightness… but the f.lux and other programs just ‘warm’ the color to give it the appearance of being dim.

    I agree that having something that could actually control it would be nicer… but I’m still looking myself…


  • Moderator

    Perhaps an easier method might be to change the color of the elements to a lesser bright white, much like the current ‘dimmed’ style. While this does not change the light output of the screen, it will reduce the brightness of the actual text being displayed. Just a thought … I started playing with a light sensor not too long ago and it doesn’t take much to adjust the DOM based on the sensor’s output.


  • Module Developer

    @KirAsh4 My problem isn’t the brightness of the text but the brightness of its background (i.e. the screen) as this can be seen at night when there’s very little light inside the room the mirror is in.


  • Moderator

    I get that, mine does the same at night. Even turning off the output, the back light is still on. Turning off the HDMI would do the trick, except after a few seconds I get that ugly, bright blue, ‘NO SIGNAL’ box. Annoying, but at least it goes away after a while and the screen’s back light will shut off. AFAIK there is no way for the rpi to control screen brightness, at least none that I could find.

    For those electrically inclined, one possible hardware solution is to tap into the brightness control within the monitor, and tie that to the rpi with a light sensor. It’s easier for those who buy their controllers off of eBay as those things are exposed and easy to get to, but on a sealed (box purchase) monitor, you’d have to tear it apart and probe for the signals that control the back light.


  • Module Developer

    @KirAsh4 That would indeed be a great solution. Will ask one of my friends to have a look into that, maybe he can tap into the brightness settings this way.

    As I don’t have my mirror put together at this stage (It’s just a screen attached to a Pi), have you tried lowering the brightness at night so that only the text is visible but not the screen? So what I’m asking is: is controlling the screen brightness the key to hiding the screen at night or does the text become illegible if we do that?


  • Moderator

    I have not.


  • Module Developer

    @KirAsh4 Well, if you ever feel like experimenting, let me know :)


  • Moderator

    Not any time soon. I’m coping with a family loss at the moment and haven’t touched anything in 3 weeks.


  • Module Developer

    @KirAsh4 Sorry to hear that. All the best for you.


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