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I don't know why, but I'm unable to set the brightness to more than 30%.

The package xbacklight does receive the command to set brightness at 100%, but it never actually happens.

Interesting fact: if I'm using the laptop without the battery and remove the charger for a second, the brightness spikes to the true 100% state briefly.

brightness settings reveals that brightness is around 30%, actually:

brightness-settings

lsb_release -a:

Distributor ID: Ubuntu
Description:    Ubuntu 20.10
Release:    20.10
Codename:   groovy

/etc/X11/xorg.conf:

Section "Device"
    Identifier  "Intel Graphics" 
    Driver      "intel"
    Option      "Backlight"  "intel_backlight"
EndSection

lspci:

00:00.0 Host bridge: Intel Corporation Core Processor DRAM Controller (rev 02)
00:02.0 VGA compatible controller: Intel Corporation Core Processor Integrated Graphics Controller (rev 02)
00:19.0 Ethernet controller: Intel Corporation 82577LM Gigabit Network Connection (rev 05)
00:1a.0 USB controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 05)
00:1b.0 Audio device: Intel Corporation 5 Series/3400 Series Chipset High Definition Audio (rev 05)
00:1c.0 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 1 (rev 05)
00:1c.1 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 2 (rev 05)
00:1c.2 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 3 (rev 05)
00:1c.3 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 4 (rev 05)
00:1d.0 USB controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 05)
00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev a5)
00:1f.0 ISA bridge: Intel Corporation QS57 Chipset LPC Interface Controller (rev 05)
00:1f.2 RAID bus controller: Intel Corporation 82801 Mobile SATA Controller [RAID mode] (rev 05)
00:1f.3 SMBus: Intel Corporation 5 Series/3400 Series Chipset SMBus Controller (rev 05)
00:1f.6 Signal processing controller: Intel Corporation 5 Series/3400 Series Chipset Thermal Subsystem (rev 05)
01:00.0 Network controller: Qualcomm Atheros AR9485 Wireless Network Adapter (rev 01)
02:00.0 Network controller: Broadcom Inc. and subsidiaries BCM43224 802.11a/b/g/n (rev 01)
03:00.0 SD Host controller: Ricoh Co Ltd MMC/SD Host Controller (rev 01)
3f:00.0 Host bridge: Intel Corporation Core Processor QuickPath Architecture Generic Non-core Registers (rev 02)
3f:00.1 Host bridge: Intel Corporation Core Processor QuickPath Architecture System Address Decoder (rev 02)
3f:02.0 Host bridge: Intel Corporation Core Processor QPI Link 0 (rev 02)
3f:02.1 Host bridge: Intel Corporation 1st Generation Core i3/5/7 Processor QPI Physical 0 (rev 02)
3f:02.2 Host bridge: Intel Corporation 1st Generation Core i3/5/7 Processor Reserved (rev 02)
3f:02.3 Host bridge: Intel Corporation 1st Generation Core i3/5/7 Processor Reserved (rev 02)
  • I wrote an answer on this topic for a prior release (cosmic or disco) on laptop/device brightness, and how the various commands (I provided them in the answer) work for maybe 85% of the machines tested on, but do nothing on different hardware/chipsets, thus if the default doesn't work for you, you just vary the commands for other options (in the answer it was using a shortcut to provide brightness/backlight etc control given inbuilt didn't work on the OP's box). I can't find the answer (maybe deleted), but you've answered your own question so I didn't look long. – guiverc Feb 15 '21 at 00:22

2 Answers2

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Check if some desktop power manager overrides those settings. I don't know for Lubuntu / LXDE, but in Xfce and in KDE there is a "power manager" applet where reducing screen brightness can be defined for various power scenarios: On wall power, on battery, on low battery, on critically low battery.

https://manual.lubuntu.me/stable/3/3.2/3.2.12/power_management.html

Then there are various suggestions here:

Brightness problem Ubuntu 18.04 LTS

HTH

HuHa
  • 3,385
  • I just realized it is a bug, thanks to the first link! I'll make an update on question body, so you know how it bugged. – doctrineplant Feb 14 '21 at 22:41
  • I made an answer, instead. – doctrineplant Feb 14 '21 at 23:03
  • Lubuntu hasn't used LXDE (or GTK2) since 18.04, but the question is about a groovy system thus LXQt and Qt5 base. What has LXDE got to do with it? – guiverc Feb 15 '21 at 00:18
  • @guiverc: Whatever, if you had read what I wrote you would have realized I gave the hint to check the desktop's power manager applet. Don't sidetrack with irrelevant stuff here. – HuHa Feb 15 '21 at 12:38
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lxQt Brightness Settings has a master slider, which is used to define the maximum brightness possible for all monitors.

Although, for some reason, I can't use this slider if launching lxQt Brightness Settings from any other place then terminal ($ lxqt-config-brightness).

Because of that, everytime I would try to increase the value of this master slider, the setting wouldn't be saved and master slider get back to 30%.

As of now, I have launched the applet from terminal and set master slider to 100% and now, I can use 100% brightness on my monitor.

I have no idea why this applet is not working as intended.

here's the applet master slider I'm talking about