There’s an expression about knowing just enough to be dangerous. In the case of sleep science, Apple may know just enough to disappoint. In 2016, it introduced an iOS feature (later added to MacOS) called Night Shift that can change the screen to a “warmer” (orangey) hue before bedtime. The aim is to reduce the blue light that blocks the production of the sleep-inducing hormone melatonin. But a new study by the Rensselaer Polytechnic Institute in New York State shows that Night Shift’s effect on melatonin is negligible, although the color change could have a psychological effect. And other factors, like screen brightness and a preoccupation with what’s on the screen, can also keep people awake.
First some background: researchers established in a 2013 study that looking at a tablet screen at night would push down melatonin. They tested subjects using an iPad 2 and found that melatonin production dropped 23% after two hours of looking at the screen.
Mariana Figueiro, director of Rensselaer’s Lighting Research Center, worked on the original study and directed the latest, which tested the effect of Night Shift at the two extremes of its color adjustment slider. In the “Less Warm” setting, which is close to the standard screen hue, melatonin fell by 19% after two hours of using an iPad in the evening. In the “More Warm” setting, which is about the color of light from an incandescent bulb, melatonin dropped 12% . At first, it may look like Night Shift is helping, but these differences fall within the margin of error. “Basically having the night shift at any mode is not statistically significantly different than not using it,” says Figueiro.Even if it’s reducing melatonin suppression, Night Shift isn’t stopping it completely, and the amount it helps is unclear. “Right now no one knows if 1%, 10%, 20% melatonin suppression is [significant],” says Figueiro. “There is a camp in science that says you have to have zero suppression.” The amount of time makes a difference. After just one hour of iPad use, melatonin was suppressed only 15% in less warm and only 8% under more warm.
The research findings were hard at first to square with personal experience and an informal poll of friends who all say that Night Shift helps them fall asleep. They described the warm tones as relaxing or easy on the eyes. Figueiro agrees that the color shift might have a psychological effect; it’s just not appreciably affecting melatonin levels.
Figueiro suspects that the screen’s brightness may be at least as important as its hue. That’s (somewhat) good news for people who stare at smartphones instead of tablets. While she hasn’t done studies with phones, Figueiro has calculated the amount of light that a typical smartphone screen puts out. “From our calculations, it is not sufficient to suppress (melatonin),” she says. Getting wrapped up in whatever is on the screen can still keep people awake, however.
In all the studies, the iPad was set to maximum brightness. “But they’re not sitting there looking at a white screen,” says Figueiro of the research subjects. “Some of them were watching movies, some of them were doing Facebook, so there’s this huge variance in how much light they’re actually getting…[Our approach was] let’s just let people do what they normally do.” (The latest study retained the iPad 2s, for consistency.)Next, Figueiro wants to study the effect of different brightness levels, to see if the combination of warm color and dim light makes a difference. Although there are practical limits. “To drop the light level and to put it in the more warm [mode]…when I do that, I can’t see anything,” she says. “It’s really, really awful.”
Regardless of the screen’s color and brightness, the content on it also affects sleep. A preoccupied mind will have a difficult time falling asleep, whatever the circumstances. “[If] you’re looking at your bank account, and you don’t have enough to pay your bills, you’re not going to sleep that night,” says Figueiro. “So melatonin is only one part of sleep, but it’s not the whole story.” Her advice, unsurprisingly, is to just turn the device off before bed.