Question: I have Blank screen disabled but my PC seems to be ignoring this. This issue also ignores the [Caffeine](https://extensions.gnome.org/extension/517/caffeine/) extension. This is pretty recent behavior as it's been working for a long while now.

[![Power settings](https://i.stack.imgur.com/6nLZm.png)](https://i.stack.imgur.com/6nLZm.png)

Disabling idle-dim in dconf seems to have done it.

Answer: 
This is from another [answer](https://askubuntu.com/questions/1000734/prevent-a-workstation-screen-from-dimming/1000745#1000745) I posted recently. You may not need the Login screen section.

Terminal CLI method
===================

To prevent screen from turning off you need two settings, one under battery power the other when plugged into wall outlet (A/C).

For battery timeout:
--------------------

```
gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout <time_in_seconds>

```

For AC timeout:
---------------

```
gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout <time_in_seconds>

```

So for both Battery and A/C set the time to 0 (never).

For Login screen:
-----------------

```
gsettings set org.gnome.desktop.screensaver idle-activation-enabled false

```

Disable dimming screen when idle:
---------------------------------

In [Unix & Linux](https://unix.stackexchange.com/questions/257329/laptop-screen-dims-after-20-seconds-cannot-change-that/258886) someone complained when on battery screen dims every 20 seconds and wants to turn that feature off:

```
gsettings set org.gnome.settings-daemon.plugins.power idle-dim false

```
Nothing in the accepted answer has worked for me in 18.04. Instead I had to do the following:

```
gsettings set org.gnome.settings-daemon.plugins.power idle-brightness 100

```

Note that this doesn't set the idle to 100% of the max but 100% of the current setting (at least I think that's what it's doing). If you have your screen dimmed already it will stay dimmed.