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Issue 360042 Consider using single user-set brightness level instead of separate ones for AC and battery
Starred by 3 users Project Member Reported by, Apr 4 2014 Back to list
Status: Verified
Closed: Apr 2014
NextAction: ----
OS: Chrome
Pri: 2
Type: Bug

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powerd currently maintains two user-specified panel backlight brightness levels, one used while on AC power and one for battery. The former is always greater-than-or-equal-to the latter: if you hold the brightness-up key while on battery power, the stored AC brightness is also increased as soon as the battery brightness would exceed it.

I'm not sure that it makes sense to track two separate levels after the user has started adjusting the brightness -- that's a clear sign that they have a strong preference for a specific brightness. I run into this frequently when I adjust the brightness to the lowest level while on battery power in a dark room and then get blinded when we jump to 80% after I plug in the charger.

I propose preserving the existing default percentages (63% and 80% for battery and AC, I think) but only switching between them automatically if the user hasn't touched the brightness keys since the system booted. After the user adjusts the brightness, we should just track their requests as a single level instead of keeping a separate level for each power source.

(The policy being tracked at issue 310429 would still support separate AC and battery levels, of course.)
I think that separate brightness settings for AC and battery are a useful feature *if* these get persisted across reboots. You can make the screen bright while working on your desk and have it automatically dim whenever you unplug the power adapter. But this kind of micro-management only really makes sense if the settings will be preserved across reboots. If you have to re-adjust brightness after every boot anyway, I agree that there is not much value in managing two separate settings and having Daniel blinded when he plugs in his AC adapter.
Comment 2 by, Apr 20 2014
Status: Started
Project Member Comment 3 by, Apr 22 2014
Project: chromiumos/platform/power_manager
Branch : master
Author : Daniel Erat <>
Commit : ab17d5bd19d4bd57fcf3fe0bbc11f2266b4c42c7

Code-Review  0 : Daniel Erat, chrome-internal-fetch
Code-Review  +2: Chris Masone
Commit-Queue 0 : Chris Masone, chrome-internal-fetch
Commit-Queue +1: Daniel Erat
Verified     0 : Chris Masone, chrome-internal-fetch
Verified     +1: Daniel Erat
Change-Id      : I4ec6975fa058f66d8d3eaea503df122073653fc6
Reviewed-at    :

power: Use one user-set brightness level for battery and AC.

When the user adjusts the brightness because it's too bright
or too dim, they probably don't want us to change it later
just becuase they plugged or unplugged their charger.
Instead of tracking separate user-set brightness levels to
use while on battery and AC power, make powerd use the same
level for both.

The default brightness level still differs between the two
power sources, and Chrome is able to request different
levels via policies that it sends to powerd.

TEST=manually checked that brightness doesn't change when
     plugging or unplugging charger after manually setting
     the brightness; also updated existing tests

We shouldn't make changes like this without looking at the power impact, as this is going to increase power usage on battery. 

+Sameer for thoughts.
Comment 5 by, Apr 22 2014
The default levels are unchanged; this change only affects users who have adjusted the brightness to the level that they want.
Comment 6 by, Apr 22 2014
According to stats Power.UserBrightnessAdjustmentsPerSessionOnBattery & Power.UserBrightnessAdjustmentsPerSessionOnAC no more than 15% of current users adjust their backlight setting during a session.  

Of those making the change on battery most (12%) make adjustment to 100% brightness ( Power.BacklightLevelOnBattery )

This change will likely help those who appear to already be keeping brightness at 100% avoid raising it manually when transitioning from AC to battery.

As for power impact operating at 100% (vs 63%) on 200nit display is roughly 1W or 16% decrease in battery life for a 6Wavg system.
Comment 7 by, Apr 23 2014
Status: Fixed
Comment 8 by, Sep 17 2014
Status: Verified
37 is now stable.
Project Member Comment 9 by, Jul 15
Labels: merge-merged-release-R53-8530.B
The following revision refers to this bug:

commit a0c70208ce1cd093e07937ea67830efcf119a0b7
Author: Nicolas Boichat <>
Date: Thu Jul 14 10:04:56 2016

Project Member Comment 10 by, Jul 15
Labels: merge-merged-release-R52-8350.B
The following revision refers to this bug:

commit 93f777a4ab2a04ff8776bdc9a4a1361e0a37c379
Author: Nicolas Boichat <>
Date: Thu Jul 14 10:04:56 2016

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