Ubuntu – Change the brightness adjustment interval

brightnessdisplay

So whenever I hit my dim/brighten keys on the keyboard, a notification bubble pops up with the screen brightness. All that's fine, but I would like to be able to change how much the brightness changes with each key press.

For example, right now it takes just 5 presses to go from the completely dark to the brightest setting. However, I know from the "Brightness/Lock" setting that the screen is capable of much smaller intervals than this.

Is there a way to change how much the brightness jumps each time the keys are pressed?

Best Answer

Since you haven't specified which desktop environment you use, I'll provide some KDE-specific details as well.

I've just updated KDE to 4.9.2 and met with the same inconvenience. I decided to dig into the code, and here are my conclusions:

  1. Brightness is actually controlled by kernel itself. According to KDE's PowerDevil source code, there exist two basic ways for kernels to provide control interface:
    • sysctl() system call (likely on *BSD systems, I suppose)
    • sysfs interface (likely Linux)
  2. sysfs interface is located at /sys/class/backlight/*your_backlight_type*/. Here's what it looks like for me:
    $ ls -1 /sys/class/backlight/intel_backlight/
actual_brightness
bl_power
brightness
device
max_brightness
power
subsystem
type
uevent
    Two files are relevant for us now: brightness and max_brightness. And here's how they can be used:
    $ cd /sys/class/backlight/intel_backlight
$ cat max_brightness 
976
$ cat brightness 
176
$ echo 77 | sudo tee brightness
77
    First command lets you determine the maximum brightness you can set (the minimum is always zero). Second one lets you know what value the actual brightness is set to. And with the third you can set it to any value you desire in the range of [0; max_brightness].

  3. KDE's KRunner still has the freedom to set any brightness level. Press Alt-F2 and type:

    screen brightness 17

  4. KDE's keyboard Brightness Up and Brightness Down key handling code has increment value of 10% hard-coded. Hence, unless you want to mess with building KDE from sources, there's nothing you can do with it.

  5. KDE's BatteryMonitor plasmoid has its own brightness control, whose increment is also hard-coded as 10%, but now we're lucky enough, since it is written in QML: $ sudo nano /usr/share/kde4/apps/plasma/plasmoids/battery/contents/ui/PopupDialog.qml (upd: in KDE 4.11 it has been moved to BrightnessItem.qml), navigate to section that looks like

    Components.Slider {
        id: brightnessSlider
        minimumValue: 0
        maximumValue: 100
        stepSize: 10
        onValueChanged: brightnessChanged(value)
    }
    and change the step size to what you desire. After relogin you'll see the change.

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