iOS’s Night Shift is just the latest entrant for color-temperature shifting, albeit making it available to roughly 500 million devices via iOS 9.3. Only devices released starting in about 2013 have hardware that supports the feature, according to Apple’s feature notes.
But the big problem is that there’s no solid evidence that mobile screens’ color temperature is the real culprit, nor whether devices and monitors can shift enough to matter if they were—or even if blue light on its own is the trigger.
While expose to colors of light has been well researched, it’s not entirely clear that merely seeing light heavy in the blue part of the rainbow is the trigger—or at least the sole trigger. It may be that a shift in color in the hours around twilight, which comes with a change from blue to yellow, could be a more significant marker. Blue may be a red herring.
It might also be the intensity of light or the proportion of the visual field it occupies. A large, bright screen that’s far away could have as little or the same effect as a small, bright screen close up. Many of the studies until recently used full-room illumination or specifically-tuned light sources (like panels used to treat seasonal affective disorder), and have taken place in highly controlled laboratory environments that block all other light. Because of the cost and complexity of the experiments, the most rigidly constructed ones often involve only a dozen or so individuals who spend several days under observation.
In terms of size and brightness, it’s more likely that an effect on melatonin production would come from adjusting an iPad Pro than an iPhone of any size, due to light and intensity of light produced.
Mariana G. Figueiro, a professor at Rensselaer Polytechnic Institute and the program director of its Lighting Research Center, says her group has used precise measurements of light sources and displays to calculate predicted effects and performed clinical testing to test outcomes.
She notes there’s a huge variation between an iPhone, a tablet, and large-screen televisions. “People tend to have a misconception that because it looks bright, because your visual system is so sensitive, that it is affecting your melatonin,” she says. Her work and that of others has shown you “can still suppress melatonin with a warm color if it’s a high light level.”
Even what’s being displayed matters. Dr. Figueiro says a Facebook page with a white background and mostly text produces more light than the same page viewed with white on black text.
Although she hasn’t tested Night Shift yet, she says that in terms of size and brightness, it’s more likely that an effect on melatonin production would come from adjusting an iPad Pro than an iPhone of any size, due to light and intensity of light produced.
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