Night Shift is a new feature included in the update of Mac OS Sierra to version 10.12.4. If activated, the colors on the screen hotter after sunset, which according to Apple reduces the blue light and can help you come to rest better at night.
However, the reduction of the blue light is really only marginal, writes one of the developers of Macprogrammet Flux, which for many years has given Mac users a similar function.
The figure above shows the measured reduction of blue light with the Night Shift activated (according flux measurement). In the picture below, the corresponding decrease of flux. Both use the default settings.
Flux developer writes that Night Shift makes colors look as warm (orange) like Flux, but it hides a lot of blue-green light that is not obvious to our view despite the fact that it affects the brain's perception of day and night. Flux has done a test where subjects can see displays with a filter in front of either removing the 10 or 99 percent of the blue-green light, and they could not see any difference.
Another reason that Flux is critical to Apple implementation on Mac OS is to the strongest setting admittedly reduces the blue-green light more, but at the same time actually increases the overall brightness, which takes away much of the potential health effects.
Flux is free and works with many older Macs that either can not run Mac OS Sierra, or have not received the Night Shift.