Screen doesn't dim when power switches to battery

**Toz** · September 8th, 2013

Originally Posted by ooddiittyy

That absolutely did the trick! Thank you very much; I really appreciate the guidance. As an aside, it's curious to me why this isn't enabled by default. Do you happen to know the thinking?

A few reasons come to mind as to why its not working automatically:
1. If you have more than one backlight interface, the system may be confused as to which one to use.
2. If you have laptop-mode tools installed, you may need to look closely at the configuration file and make sure its setup correctly.
3. The power manager for your DE (Gnome, Unity, Xfce, etc) may not be properly managing the backlight interface.

**Bjornen** · October 27th, 2013

THX Toz. This worked out of the box for me

**muhammad4** · September 25th, 2014

Awesome! It worked indeed.

**mohsen-forghani** · January 11th, 2015

great thanks, it works

**thethakuri** · January 21st, 2015

First of all, thank you for your solution, it works. However I have couple of questions:
1. In step 2, you have asked to, "To find out which one is the active one, echo a value between 0 and the second value above (max_brightness) to the brightness file". I have three backlight interface and all of them seem to be active. However I used acpi_video0 in the zzzbattery file and it seems to work. So, it is okay to ignore the remaining two interfaces even though they seem to be active as well ?
2. Secondly, when the the power profile changes (i.e. when power is turned off or on), there is a delay of few secs before the right measure is applied. Is it normal for Ubuntu ? In windows it seems to be a little bit swifter.
Cheers !

**Toz** · January 22nd, 2015

Originally Posted by thethakuri

So, it is okay to ignore the remaining two interfaces even though they seem to be active as well ?

Yes. Although they are present, they don't seem to be the active ones.

2. Secondly, when the the power profile changes (i.e. when power is turned off or on), there is a delay of few secs before the right measure is applied. Is it normal for Ubuntu ? In windows it seems to be a little bit swifter.

When the power profile changes, a number of scripts are run. Have a look at /var/log/powersave.log to see the sequence. You can try renaming zzzbattery to make it run earlier (the scripts are run in alphabetical order). The only thing to keep an eye on is if it gets reversed once again by one of the other scripts that may be affecting the brightness level. Moving it up in the execution order may have it execute quicker.

And btw, welcome to the forums.