A group that used Night Shift and reduced brightness, however, saw melatonin reduced by only 12%. Those who used Night Shift with their screen brightness at a standard level had their melatonin reduced by 19%. Subjects who used the iPad on regular settings (without Night Shift) had their melatonin levels reduced by 23%. What they found was that melatonin was decreased under all of the conditions.

on four separate nights under four experimental conditions, including a group that used the iPads’ Night Shift feature. Figueiro recruited 12 young adults to view iPads between 11:00 p.m. In the study, LRC researchers Rohan Nagare, Barbara Plitnick, and Mariana G.

But, does it work? Researchers from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute looked into the issue. In theory, reducing the blue light should help the problem with suppression of melatonin. There are apps for the Android operating system that work in a similar way. The Night Shift mode permits users to change the screen’s color to “more warm” (i.e., less blue light) or “less warm” (i.e., more blue light), without necessarily changing its brightness. In an effort to address this problem, Apple released the Night Shift application for its line of smartphones and tablets. Exposure to what some call “light at night” (or LAN) can acutely suppress melatonin, a hormone produced at night and in darkness, which tells the body it is nighttime. The main concern is over the short-wavelength “blue” light emitted by smartphones, tablets, and even televisions. I guess that's better than the PC behavior where even if you switch the source on the display back to the Mac, Windows still thinks its connected and continues to extend the display (the fix for that is to go to display properties and select 'only show on display 2') , but thats a whole other gripe.The light emitted by portable electronic devices (PEDs), particularly when used at night, has drawn a great deal of interest recently. I then have to move everything back to the big display. The application all stay on the laptop screen and the big screen is empty when I switch the source back on the monitor. Prior to macOS Big Sur, if I switched to the PC input on the monitor, all the macOS windows would shift over to the built-in laptop display, and then shift back to their correct window once I switched back. Each computer also has its own dedicated monitor (built-in for my Macbook, an old external for my PC). I switch between the two sources on the monitor depending on what I'm doing. I have one big 4K monitor, connected to both my Mac (USB-C) and my PC (HDMI). I've found something thing macOS Big Sur broke - the 'recovery' after changing display sources.

Night shift mac app