It is widely accepted that the blue light emitted from bright screens, like the one you’re staring at right now, can have a negative impact on sleep.
Many people are using blue light filters to lower the amount that they are exposed to in order to improve their quality of sleep.
Ubuntu 18.04 (since GNOME 3.24) has such a filter built-in. Here's how it works.
1 Screen Display
Open the GNOME Launcher and click on Settings. Select Screen Display and then Night Light.
2 Night Light
Note: By default this setting will be off.
3 Enabling the Filter
The options are Sunset to Sunrise or Manual.
Setting to Manual as per the example above, will allow you to customise the From - To times to limit the amount of blue light in the evenings.
Setting to Sunset to Sunrise will automatically adjust the blue light taking into account your timezone settings.