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Not Such a Bright Idea: Why Your Phone's ‘Night Mode’ May be Keeping You Awake

posted by Fnord666 on Thursday December 19 2019, @08:42AM   
from the the-blues-may-be-good-for-you dept.

"upstart" writes:

Submitted via IRC for chromas

Not such a bright idea: why your phone's 'night mode' may be keeping you awake

"Night mode" is one of those features you may be aware of only because your phone keeps telling you about it. At some point while you are lying in bed at night sending texts, your screen may politely suggest you activate a function that shifts the colours of your screen from the colder to the warmer end of the spectrum. It is supposed to help you sleep better.

Findings in a study led by Dr Tim Brown and published in Current Biology suggest this is the very opposite of correct. The research, carried out on mice, appears to rubbish the notion that blue light disrupts sleep. All things being equal, warm yellow light is worse.

[...] According to the study, brightness levels are more important than colour when it comes to stimulating the body clock. However, when the light is equally dim, blue is more relaxing than yellow.

This makes basic sense: daylight is yellow, twilight is blue, and sunrise and sunset are pretty reliable ways to tell your body clock what time it is. Of course, at this point, we only know it works on mice – and mice don't have phones. "We think there is good reason to believe it's also true in humans," says Dr Brown.

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Original Submission

• Re:The actual article - also summary is wrong (Score: 2) by All Your Lawn Are Belong To Us on Thursday December 19 2019, @02:12PM

  by All Your Lawn Are Belong To Us (6553) on Thursday December 19 2019, @02:12PM (#934203) Journal

  Well, the two issues I would note are: a) Prima facie, mice are not humans. They do discuss this in the article and believe it may apply to humans, and the argument seems cogent. But still mice are not humans. b) The article actually discusses a couple of different scenarios with different testing. The answer, however, is in the study summary you linked to. They state that while yellow-shifted colors may naturally assume to ecologically signal twilight, as sun angle drops there is actually a blue-shift to the light. Thus blue light may actually trip the circadian reset - which correlates with the biological observations they represent in the study. They note that blue light produces weaker circadian response. That's what you want if you're using lights at night - you don't want the body tripped into thinking it's suddenly daytime and you don't want the body responding in circadian rhythm to lights at night. And I think (though would appreciate correction if I'm wrong) that when they're talking circadian entrainment and alignment they are talking about recognizing when it is night / sleepy time.

  In short, I think the summaries are mostly correct. The study suggests blue light, per se, isn't necessarily bad, because what you don't want is a circadian response to artificial light ("Hey, it's daytime!")

  In humans, short-wavelength light evokes larger circadian responses than longer wavelengths [1, 2, 3]. This reflects the fact that melanopsin, a key contributor to circadian assessments of light intensity, most efficiently captures photons around 480 nm [4, 5, 6, 7, 8] and gives rise to the popular view that “blue” light exerts the strongest effects on the clock. However, in the natural world, there is often no direct correlation between perceived color (as reported by the cone-based visual system) and melanopsin excitation. Accordingly, although the mammalian clock does receive cone-based chromatic signals [9], the influence of color on circadian responses to light remains unclear. Here, we define the nature and functional significance of chromatic influences on the mouse circadian system. Using polychromatic lighting and mice with altered cone spectral sensitivity (Opn1mwR), we generate conditions that differ in color (i.e., ratio of L- to S-cone opsin activation) while providing identical melanopsin and rod activation. When biased toward S-opsin activation (appearing “blue”), these stimuli reliably produce weaker circadian behavioral responses than those favoring L-opsin (“yellow”). This influence of color (which is absent in animals lacking cone phototransduction; Cnga3−/−) aligns with natural changes in spectral composition over twilight, where decreasing solar angle is accompanied by a strong blue shift [9, 10, 11]. Accordingly, we find that naturalistic color changes support circadian alignment when environmental conditions render diurnal variations in light intensity weak/ambiguous sources of timing information. Our data thus establish how color contributes to circadian entrainment in mammals and provide important new insight to inform the design of lighting environments that benefit health.

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