Force GNOME Night Light to stay on and never turn off

Solution 1:

The "native" way for Gnome Shell to always keep your nightlight color on involves to access some hidden options in dconf-editor. dconf-editor is not installed by default on Ubuntu 18.04. You may need to install it first.

• Open dconf-editor and navigate to the key /org/gnome/settings-daemon/plugins/color/
• Set night-light-schedule-automatic to false
• Set night-light-schedule-from to 0, and night-light-schedule-to to 24 (or any value higher than this)

You can also adjust your color temperature there.

In Ubuntu versions later than 18.04, these settings are exposed in "Settings", under "Displays".

Solution 2:

I was similarly looking for a way to keep it on at all times but didn't see a way through the GUI. The other answers work but I found a simpler way to enable it via terminal without having to install any additional tools:

gsettings set org.gnome.settings-daemon.plugins.color night-light-enabled true
gsettings set org.gnome.settings-daemon.plugins.color night-light-schedule-automatic false
gsettings set org.gnome.settings-daemon.plugins.color night-light-schedule-from 0
gsettings set org.gnome.settings-daemon.plugins.color night-light-schedule-to 24
gsettings set org.gnome.settings-daemon.plugins.color night-light-temperature 5000

To get an idea of temperature value ranges, Redshift uses default values of 3700 at night and 5500 during the day.

Solution 3:

Another alternative is sct which you can install with sudo apt install sct.

$ sct -h
Usage: sct [temperature]
Temperatures must be in a range from 1000-10000
If no arguments are passed sct resets the display to the default temperature (6500K)
If -h is passed sct will display this usage information
$ 

Putting sct 3500 or whatever other value you prefer in your autostart should do it.