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List:       kde-usability
Subject:    powerdevil changing the brightness level - default behaviour
From:       Sven Burmeister <sven.burmeister () gmx ! net>
Date:       2008-12-30 19:57:30
Message-ID: 200812302057.30809.sven.burmeister () gmx ! net
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Hello!

There is a usability bug report which I (we) need your expertise on.

http://bugs.kde.org/show_bug.cgi?id=173930

Powerdevil has a certain brightness level set for each power profile. So if 
you plug-in your power, you can get 100% brightness, if your battery reaches 
25% it will switch to another profile and apply the 80% brightness that are 
set for that profile, if the battery only has 12% left it would change to yet 
another profile which has 50% brightness. If you plug-in the power, it would 
change the profile and set the brightness to 100%.

Now the question is, how powerdevil should handle the brightness, if the user 
has set it manually, e.g. via the slider of the battery applet.

Example: Battery at 70% and the user sets brightness to 20%. The battery 
discharges and reaches the 25% mark and powerdevil switches to the next 
profile, which has 50% brightness set.

The question now is, what do most users expect:
a) the brightness set manually remains the same, i.e. 20%
b) the brightness should be increased to 50%

This was for discharging, if we plug-in the power, there are again two 
possibilities, what the user might expect:
a) the brightness set manually remains the same
b) the brightness is increased to 100%

Currently powerdevil picks b) in both cases. From the reporter's an my point 
of view it should stick to a) in the first case.

Can anyone help out with some expertise? I thought my claim was straight-
forward, but apparently it's not. I assumed that if the user sets the 
brightness manually to a value lower than the current/next profile, this can 
only be for two reasons: 1. he wants to save more power than usual or 2. he 
wants to adjust the screen's brightness to the environment (dark room) or his 
eyes' sensitivity.

Hence, if the battery is discharging, i.e. the next profile is supposed to 
save more power then the one before (regarding brightness), it does not make 
sense to save less power. So in the example outlined above powerdevil should 
not increase the brightness (consume more power), but only decrease, in case 
the next profile has an even lower level set (save more power).

If I set the brightness to 20% because my environment is very dark or my eyes 
hurt, then it does not make sense to increase the brightness level either, 
because I would have to decrease it again manually, although I already did so.

If the power is plugged-in, the brightness should obviously be increased.

So it seems there are three groups of users and the question is, which one 
should be cared for by default and does powerdevil have to care for all of 
them.

1. Those that want profiles to override the manually set brightness in every 
case (current default)
2. Those that want profiles' brightness to only considered if they are lower 
than the manually set (discharging) or if the power is plugged-in.
3. Those that want their manually set brightness level to never be changed 
automatically.

I hope this did not get too confusing! ;)

Sven
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