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thinkpad t450 boot screen brightness

2019-05-16, 17:50 PM

Is there a way to adjust the screen brightness as soon as the ON button is pressed and the screen lights up? I'm using linux and i have to wait to get X started and a session opened to be able to reduce it with Fn+F5 and it does not memorise it. So i have to repeat this operation at every OS boot. By default the brightness is at the maximum.

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Re: thinkpad t450 boot screen brightness

2019-05-17, 3:51 AM

Hi itt788.

 

Welcome to our community forums.

 

Could you try these generic steps on how to set the brightness in Linux?

 

If the laptop's default brightness adjustment keys are not working, then add a boot time linux kernel parameter and try again.

 

1. First open up the /etc/default/grub file with your favorite text editor as root.

 

sudo nano /etc/default/grub

 

2.Find the line staring with GRUB_CMDLINE_LINUX_DEFAULT=, most probably there will be the word quiet also. (see the image attached).

 

3. Add a few words there, acpi_backlight=vendor all inside the double quote.

 

4. Save and exit the text editor and then reboot the laptop.

 

The acpi_backlight kernel parameter options are not just limited to vendor, and it's guaranteed to work.

 

You might have to experiment with other options like native and none . After rebooting if the brightness adjustment hotkeys are working then you can set a laptop's brightness with the xbacklight command.

 

If it's not installed, then install it with apt, sudo apt-get install xbacklight , and then run the command like below.

 

xbacklight -set 20 # set brightness to 20%


Keep us posted on how it goes.



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Re: thinkpad t450 boot screen brightness

2019-05-17, 9:51 AM
actually my post is not written clearly enough and it sounds confusing. In the title i put "boot screen" and i really mean it. The Fn+F5 key combo is meant to reduce the brightness. In my case or for all T450 this does not work before the OS has started. It's a bios related problem, it does not seem to support this function. Thus, yes i have to wait that the OS has started to be able to reduce it as fortunately it supports it. I precised linux as i've seen people complaining that in windows it didn't work. Of course i might tune linux either right from kernel boot command or user space init commands to do it automatically but this is not the point here.
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t450 boot screen brihtness

2019-05-19, 14:36 PM

this is a reposting of a previous post which was accidentally in the wrong sub-group.

 

The Fn+F5 key combo is meant to reduce the brightness. When i start the computer thebrightness is always at the maximum and pressing Fn+F5 does not reduce it. Only the OS kernel, linux in my case, allows adjusting the brightness, and only when X at started. So it's a bios related problem, it does not seem to support this function. Of course i might tune linux either right from kernel boot command or user space init commands to do it automatically but this is not the point here. 

 

Moderator note: original thread moved here.  Threads merged.

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8 Posts

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Re: t450 boot screen brihtness

2019-05-19, 15:34 PM
It seems the LCD panel model number is important. From HWiNFO the model number would be :
Monitor Name: AU Optronics [Unknown Model: AUO303E]
Monitor Name (Manuf): AUO B140RTN03.0
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Re: t450 boot screen brihtness

2019-05-19, 15:35 PM

One possibility is that the panel was replaced by one that was not an original Lenovo screen.  I know that on on T450 machines, the aftermarket screens don't have the configuration information for the panel needed to control brightness stored in the EEPROM (EDID) on the screen.


Rich


I do not respond to requests for private, one-on-one help. Your questions should be posted in the appropriate forum where they may help others as well.

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Re: t450 boot screen brihtness

2019-05-20, 15:56 PM

 wrote:

One possibility is that the panel was replaced by one that was not an original Lenovo screen.  I know that on on T450 machines, the aftermarket screens don't have the configuration information for the panel needed to control brightness stored in the EEPROM (EDID) on the screen.


so either the screen eeprom needed being reflashed or lenovo needs to provide a bios update.

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