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#1 2017-01-10 19:32:48

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Reduce brightness increment/decrement

I have a Dell XPS 15 9550 laptop now for almost 2 weeks.  I am very happy with it, but if possible I would like to tweak the screen brightness settings.

It appears I have 13 brightness levels (0 - 12):

$ cat /sys/class/backlight/intel_backlight/max_brightness
12

I first thought that at the 0 level my screen would be off, but after a few days I noticed it is just extremely dark. My sweet spot for indoors would be somewhere between the 0 and 1 levels.

Is there a way to change the amount by which the brightness increases/decreases each time I hit the brightness keys? I would prefer smaller increments (i.e. same maximum and minimum brightness, yet more levels in between).

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#2 2017-01-10 19:39:20

R00KIE
Forum Fellow
From: Between a computer and a chair
Registered: 2008-09-14
Posts: 4,734

Re: Reduce brightness increment/decrement

I'd say that if all you have is those 13 discrete levels then there is no way to get a finer control over the brightness.


R00KIE
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#3 2017-01-11 15:43:43

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Re: Reduce brightness increment/decrement

That is a shame sad

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#4 2017-01-11 16:29:53

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 19,740

Re: Reduce brightness increment/decrement

I saw this go by yesterday and found it interesting.  My laptop (Hp Envy), left to its own devices, instantiates both an ACPI backlight control and and an Intel backlight control under /sys/class.  Oddly, it is the ACPI backlight that only had a few brightness steps.  I don't remember exactly how many as I am not in front of that machine and I disable the ACPI backlight control.  The reason I do that is because  my Intel backlight gives me 4882 steps.

Not sure what you can do with this information.  Maybe investigate whether ACPI backlight is available? and maybe it has more steps?

Last edited by ewaller (2017-01-11 16:30:06)


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#5 2017-01-13 21:20:55

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Re: Reduce brightness increment/decrement

Thank you very much. That set me to think about some changes I made to my EFI boot parameters and I went on to experiment a bit. If I set

acpi_backlight=native

then I only have /sys/class/intel_backlight. But if I set

acpi_backlight=vendor

I will also have /sys/class/dell_backlight. This one has 15 steps (3 more). Unfortunately, if I set acpi_backlight=vendor I get this error on boot:

[FAILED] Failed to start Load/Save Screen Backlight Brightness of backlight:dell_backlight.
See 'systemctl status systemd-backlight@backlight:dell_backlight.service' for details.

In another post I shared the workaround I found to solve this issue by replacing vendor with native. However, it seems that for my case it might be beneficial for me to actually fix the issue instead of working around it. I am open to any suggestion.

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#6 2017-01-14 17:31:26

binch31
Member
Registered: 2017-01-09
Posts: 6

Re: Reduce brightness increment/decrement

I had the same issue with my precision 5510 (they share the same platform), updating the BIOS with the last version solved it.

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#7 2017-01-15 03:59:47

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Re: Reduce brightness increment/decrement

Thanks binch31, that indeed improved a lot. I am almost there now smile

So updating the BIOS to the latest version resulted in

$ cat /sys/class/backlight/intel_backlight/max_brightness
187

This amount of levels is observable when using the slider to adjust the brightness, but with my physical keys I only have 20 discrete steps. Also, the lowest setting with the physical keys is considerably darker (cannot actually see anything) than the lowest setting with the slider (which is dark but usable). Next to this discrepancy, I am still getting the same error on boot with acpi_backlight=vendor.

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#8 2017-01-16 14:58:22

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Re: Reduce brightness increment/decrement

So why is there a difference in number of levels between using the brightness keys and using a slider in the desktop environment (I am using KDE)?

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#9 2017-01-16 16:56:29

binch31
Member
Registered: 2017-01-09
Posts: 6

Re: Reduce brightness increment/decrement

No clue.. I'm using Gnome and I don't feel this difference.. the lowest and highest levels are the same and it seems like the slider is using the same 20 levels

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#10 2017-01-16 20:18:30

Aeronaelius
Member
Registered: 2017-01-06
Posts: 13

Re: Reduce brightness increment/decrement

I found that I can use "xbacklight -inc [number]" and "xbacklight -dec [number]" assigned to shortcuts to control the brightness interval. But this does not trigger the OSD sad

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