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[David Chatterton <dmchatterton@xxxxxxxxxx>]

Public bug reported:

This bug refers to a Dell XPS13-9333 running Ubuntu 14.10.

I discovered a workaround to prevent the screen starting with full
brightness.

The reference to the workaround advice is: 
http://ubuntuhandbook.org/index.php/2014/04/save-screen-brightness-settings-in-ubuntu-14-04/

There is a folder sys/class/backlight/intel_backlight/ containing a
number of files such as brightness, actual_brightness and
max_brightness. When using Fn-F4 & F5 to control the screen backlight,
the two files: brightness and actual_brightness respond by changing
there contents to a number which is a proportion of the contents of
max_brightness (937).

The workaround was to include the line:

    echo 569 > /sys/class/backlight/intel_backlight/brightness

at the end of the file: /etc/rc.local using gedit (where 569 is a value
noted for a typically comfortable level of backlight).

This works when doing a restart but, when logging back in after logging
out, the backlight comes on at maximum brightness.

This particular laptop has a front-facing webcam fitted. Its function
can be confirmed by running the Cheese webcam Booth. It would be a vast
improvement if the ambient brightness could be sensed by the webcam and
used to adjust the backlight brightness. Auto brightness could be
selected or not by a tick box in the Brightness & Lock section of System
Settings. Similarly, a tick box might also be provided to enable saving
of the backlight brightness when shutting down or logging off

** Affects: ubuntu-docs (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1400155

Title:
  inconsistent backlight brightness behaviour

Status in ubuntu-docs package in Ubuntu:
  New

Bug description:
  This bug refers to a Dell XPS13-9333 running Ubuntu 14.10.

  I discovered a workaround to prevent the screen starting with full
  brightness.

  The reference to the workaround advice is: 
  http://ubuntuhandbook.org/index.php/2014/04/save-screen-brightness-settings-in-ubuntu-14-04/

  There is a folder sys/class/backlight/intel_backlight/ containing a
  number of files such as brightness, actual_brightness and
  max_brightness. When using Fn-F4 & F5 to control the screen backlight,
  the two files: brightness and actual_brightness respond by changing
  there contents to a number which is a proportion of the contents of
  max_brightness (937).

  The workaround was to include the line:

      echo 569 > /sys/class/backlight/intel_backlight/brightness

  at the end of the file: /etc/rc.local using gedit (where 569 is a
  value noted for a typically comfortable level of backlight).

  This works when doing a restart but, when logging back in after
  logging out, the backlight comes on at maximum brightness.

  This particular laptop has a front-facing webcam fitted. Its function
  can be confirmed by running the Cheese webcam Booth. It would be a
  vast improvement if the ambient brightness could be sensed by the
  webcam and used to adjust the backlight brightness. Auto brightness
  could be selected or not by a tick box in the Brightness & Lock
  section of System Settings. Similarly, a tick box might also be
  provided to enable saving of the backlight brightness when shutting
  down or logging off

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