Night Shift explained
What is Night Shift actually meant to do, and does it really work?
In 2016, iOS 9.3 added a feature called Night Shift that, during the evening, “automatically adjusts colors to the warmer end of the spectrum, making the display easier on your eyes”. Since macOS 10.12.4, it’s also available on Macs (excluding those made before 2012).
There have been concerns for years about the influence of artificial light on circadian rhythm, the body’s natural 24– hour cycle. In 1996, epidemiologists Richard G Stevens and Scott Davis noted that “the normal nocturnal melatonin rise in humans can be suppressed by light of sufficient intensity.”
We now know melatonin production is regulated by cells in the retina containing melanopsin. Melatonin governs sleep patterns, and growing evidence links this and other health factors to the shift from living in sunlight all day and darkness all night to constant electrical lighting.
Compared to, say, tungsten bulbs, computer screens are skewed to shorter (bluer) wavelengths. A 2015 study, published in Public Health, found screens were getting brighter and bluer. Back in the days of CRT monitors, Macs used a yellowish 5000K color temperature, the preference of print designers. But PCs’ daylight–like 6500K became the norm for LCD displays, which then steadily increased in brightness, OLEDs going even further. Used after sunset, the screen tells your body it’s daytime.
More worryingly still, a University of Toledo study this year, published in Nature, found blue light could kill eye cells, suggesting a link to serious conditions such as age–related macular degeneration and others.
Less bright, more warm
Predating Night Shift, Mac users can vary screen brightness and temperature using f.lux ( justgetflux.com), an app made by former Google Picasa developers Lorna and Michael Herf. Michael has spent a lot of time studying the research on how light affects the body, so we asked his advice. He stressed that a small reduction in blue light isn’t enough. Night Shift roughly halves melanopic intensity, while
You can schedule Night Shift in System Preferences’ Display pane (macOS) and in Settings > Display & Brightness (iOS).
f.lux aims to reduce it by up to 90 per cent. As well as reducing brightness, the app warms the color temperature to 3400K at sunset and 1900K at bedtime.
Night Shift gets help from Auto– Brightness. This is turned on by default on iPhones and iPads, and since iOS 11 it’s less obvious how to disable it (the option is in Settings > General > Accessibility > Display Accommodations). The screen dims as your iPhone detects less ambient light, so keep room lighting low in the evening. Manually turning down the screen brightness will help further.
macOS also has auto–brightness in System Prefs > Displays > Display, but it’s less popular with Mac users, especially for anyone doing color graphics work. Without these features, you’re at risk if you work on your Mac late at night.
Doesn’t the Toledo study tell us blue light at any time of day could hurt our eyes? Turns out there’s a big ‘but’. The sun has been there since we were knee– high to a trilobyte, and it pumps out a lot more light than your iPhone ever will. “If you go outside for even one minute per day, there’s no reason to worry about using your screen,” concludes Michael.
Could we have normal color–accurate screens that use less blue light? It’s theoretically possible, by redesigning the hardware to use a different combination of wavelengths to create the same perceived colors (metamerism). Whether that would be good or not is questionable.
Some print designers keep their screens set to 5000K. They’re getting a bit less blue light, so that’s got to be good, right? Well, no. Circadian rhythms are regulated by daylight disappearing as the sun sets. Not enough daylight is as bad as too much blue light in the evening. As we increasingly spend our days indoors, 6500K screens could actually help.
This calls into question the idea of low blue light level being a health benefit at all. Due to this, features like Night Shift might be the only way to ensure screens don’t damage our health.