On: How to Sleep

[castis]

Also, if iOS, Night Shift: https://support.apple.com/en-us/HT207570

Almost everything else, Flux: https://justgetflux.com/

[Rotareti → castis]

Flux looks interesting, but it doesn't seem to support brightness adjustment. I think it's important to sync the brightness of your monitor with the brightness of its surrounding.

[Cthulhu_ → Rotareti]

The Macbook and (I'm pretty sure) most modern laptops will also adjust backlight according to environment though.

[Rotareti → Cthulhu_]

But if you are using a workstation/external monitors you still gonna need it.