I want the night light applet from GNOME shell 3.24

You can install redshift from the following command:

sudo apt install redshift

You can just add redshift to your startup if you are OK with redshift pulling its own default settings. Or, you can configure it manually like I have laid out below.

You can get your Longitude & Latitude from https://www.latlong.net/

You can then create a config file that redshift will use in your home folder at ~/.config/redshift.conf. Add the following lines to it, and I added the lat and lon for Portland, OR. But you can add the ones for your location. Make sure to set location-provider= to manual then if you want to use the LAT and LONG. However, the application geoclue2 should be able to find your location. Change the temp-day and temp-night to your likings.

~/.config/redshift.conf

; Global settings
[redshift]
temp-day=6500K
temp-night=3500
transition=1
gamma=1.000:1.000:1.000
location-provider=geoclue2
adjustment-method=randr

; The location provider and adjustment method settings
; are in their own sections.
; These are the location for Portland, OR.
[manual]
lat=45.523062
lon=-122.676482

Then all you have to do is to add just the application of redshift -c ~/.config/redshift.conf to your startup applications and it will use your config file at startup by default.

You can check your redshift parameters by running redshift -pv or redshift -p:

terrance@terrance-ubuntu:~$ redshift -pv
Location: 45.55 N, 122.68 W
Temperatures: 6500K at day, 3500K at night
Solar elevations: day above 3.0, night below -6.0
Brightness: 1.00:1.00
Gamma (Daytime): 1.000, 1.000, 1.000
Gamma (Night): 1.000, 1.000, 1.000
Solar elevation: -22.482371
Period: Night
Color temperature: 3500K
Brightness: 1.00



terrance@terrance-ubuntu:~$ redshift -p
Period: Night
Color temperature: 3500K
Brightness: 1.00

Hope this helps!