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How to get backlight on my Acer Extansa 5220 laptop to lower than minimum brightness level?


Minimum backlight level is not as dim as I want. I want to be able to tune it to arbitrarily low level, for example to be hardly visible in a dark room (but still visible).


In my digital camera I've implemented switching off and on backlight fast enough so it looks very dimmed.


How to do it in my laptop? It uses some intel video card, so aticonfig is no use.


Tools like "Dimmer" (that just makes pixels darker colour, attempting to "fix" excess brightness by filtering it in LCD) are not acceptable: even screen with all pixels set to black looks too bright.


Expected ways:



  1. Fast enough repeated low level switching it on and off (not xbacklight/xrandr/other_things_that_turn_off_display). Only backlight, not LCD itself.

  2. Modifying something by hardware means (e.g. installing additional switch and resistor), if it is simple and safe.


Pressing Fn+F6 does almost what I want from "Low level switching", but I cannot "press" it programmatically.



Answer



Use acer_ec.pl script to control laptop's Embedded Controller.


http://aceracpi.googlecode.com/svn/trunk/acer_ec/acer_ec.pl


acer_ec.pl := 84 $VALUE_FROM_00_to_ff


It allows setting backlight a lot lower than the minimum (and a bit more than the maximum).


Of course the image quality is worse than when backlight is in normal range.


Warning Before using acer_ec on other laptop check that 84'th register is that you need. The script looks like one that can permanently damage the device if used without caution.


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