Mac Night Shift
Even better than Siri on Mac is support for a night mode on Mac. Apple brings Night Shift from iOS 10 to the Mac with Mac Night Shift.
This feature changes the temperature of your screen, making it look warmer. This means less blue light and a more orange look overall. It can help ease the transition from looking at a screen to going to sleep.
You can access it by going to the Notification Center on Mac with a two finger swipe in from the right. Pull down slightly to see the Night Shift option. Toggle this on and off.