The screen of my laptop (Dell XPS 15) is rather blue. I found that I can tweak it a little bit with redshift. During the day, 6000K is the perfect temperature, in the evening I tend to use 5500K.

Ubuntu has the Night Light option, so I was wondering if I just can reconfigure the day and night colors to be the ones I now manually set with redshift. Because redshift does not persist the settings. Even after just closing my laptop, those settings are gone.

So how can I configure Night Light for both day and evening temperatures?

UPDATE

As described here, it's possible to configure the NIGHT color using the following command:

gsettings set org.gnome.settings-daemon.plugins.color night-light-temperature <temperature>

But is it also possible to configure the DAY color as well?

I just installed 18.04.

Night Light is active, but the mouse cursor is not "red-shifting". I am using the default 'DMZ-Black' cursor theme.

But the pointer outline is a glaring bright white color, the same as when Night Light is turned off.

Is there a way to get the mouse cursor to honor the Gnome Night Light setting? (I do not want to install a different cursor theme).

Background: More red / Less blue at night

To save the eyes at night, adding more red and/or subtracting blue, is becoming popular in Windows 10 (blue-light filter) and Linux; Gnome Desktop (Night Light) and Ubuntu Unity Desktop with add-ons such as Red Shift or f.lux.

I'm wondering how to accomplish the same with Ubuntu's built-in command line xrandr <monitor> --gamma 1:1:1 feature. The 1:1:1 represents percentage of red:green:blue. I presume 1 = 100%. I'm not sure if the above packages add more red (1.2:1:1) for ~20% increase or reduce blue (1:1:0.8) for ~20% decrease or both for ~40% change.

Gnome Night Light example doesn't help

According to OMG Ubuntu, within Gnome's Night Light you can use these numerical values:

• 1000 — Lowest value (super warm/red)
• 4000 — Default night light on temperature
• 5500 — Balanced night light temperature
• 6500 — Default night light off temperature
• 10000 — Highest value (super cool/blue)

To test these numerical values, how would does one translate them to override the default --gamma 1:1:1?

What xorg's documentation says

Xorg's documentation doesn't say very much about --gamma controls:

−−gamma red:green:blue

• Set the specified floating point values as gamma correction on the crtc currently attached to this output. Note that you cannot get two different values for cloned outputs (i.e.: which share the same crtc) and that switching an output to another crtc doesn’t change the crtc gamma corrections at all.

Floating decimal points will be helpful because the script I want to upgrade sets xbacklight brightness slowly once a minute over a 90 to 120 minute transition period at dawn and dusk. I want to enhance the script with both xrandr --brightness software support for external monitors and OLED built in displays and xrandr --gamma support for red light / blue light filters. Xorg doesn't say how many decimal positions are supported but I think I think I will set bc calculations should be to 3 or 4 decimal positions for readability / precision balance.

Summary

I'm hoping to mimic what "the big guys" at Microsoft and Gnome are doing with their "more red" and/or "less blue" techniques. I haven't delved into Wayland yet but answers using that system will also be appreciated as it will no doubt be a future concern.

What adjustment to --gamma 1:1:1 are appropriate for night time?

Is it possible to configure Redshift so that screen color changes at fixed hours regardless of actual Sun position? I'm using Redshift 1.10-5ubuntu1 on Ubuntu 16.04 and GNOME.

I have geolocation turned off in Ubuntu 15.10. Is there a way to set location via GPS coordinates or neatest metro area using the in ~/.config/redshift.conf?