Should Macs start a Night Shift?

For some, the only new feature in macOS Sierra 10.12.4 is the arrival of Apple’s Night Shift on Macs. Although it is not the only new feature by any means, if you aren’t interested in cricket and don’t use Shanghainese, it might seem that way. So what good is Night Shift: is it worth using on your Mac?

Night Shift, which has been available for some time on iOS devices, changes the display output to make it appear ‘warmer’ (less blue, more red) during specified hours. Used conventionally, you’d set it to change to that warmer spectrum during the night, from local sunset to sunrise. It is easy to try out: once you have the 10.12.4 update installed, open the Displays pane, select the Night Shift tab, and tick the Manual box to turn it on until sunrise.


The theory behind Night Shift is based on our still very limited understanding of sleep and our daily body (‘circadian’) rhythms. Over the last couple of years, there has been some evidence that wakefulness is encouraged by bluer light, such as that from natural daylight, and that sleep is encouraged by redder light and darkness, as we might ‘naturally’ experience during the night.

Performing research on this area is difficult, because there are so many confounding variables. Most of us tend to be more physically active and more likely to go outdoors during daylight, and much of the populations of North America and Europe experience marked seasonal differences in daylight – both its duration and intensity. Over the last century, most of us have lived with quite bright artificial lighting, which in winter can be lit for much or all of the daytime.

Simplified (and sometimes quite inaccurate) accounts of this research often refer to different light spectra ‘setting’ our ‘body clocks’, which is not what the research actually shows. Furthermore, in real life many people sit in front of the quite bright light emitted by TVs, and there is great variation in the intensity and spectra of artificial lighting to which we are exposed during the evening.

Apple words the Night Shift blurb very carefully, with the emphasis on the word may. You may find that Night Shift helps your body adjust better to the time of day, allowing you to sleep more easily, and to find that sleep more refreshing. There is – as yet – no published scientific study which suggests that Night Shift, or the third-party tool f.lux which claims to do the same thing, provide any benefit whatsoever.

Equally, there are no grounds for thinking that Night Shift, or f.lux, would do any harm.

Unless, of course, your Mac work is colour-critical. If you are working with images, particularly if you are adjusting or correcting their colour, then you should ensure that Night Shift is turned off, or you could produce some very odd-looking work.

Night Shift, if it makes sense anywhere, is probably most useful on displays which you use late in the evening, in the hour or two before going to bed, and any which you might use in bed at night. It is therefore probably less useful to anyone on a Mac, than on an iPhone or iPad. But it is now available, and free.

There is one little irony here, though: one issue which current research has identified as being fraught when it comes to sleep is night-work. If you have ever worked shifts through the night, you will already have experienced some of the problems which that brings. If there’s one term which is associated with short, fretful, and poor-quality sleep, it is night shift – probably not the best name for the feature.