The headline doesn't reflect the content:
"Although iPads were used in this study, researchers also measured other devices that emit blue light, including eReaders, laptops, cell phones and LED monitors."
So, they did a user study using iPads, and only measured the other devices. They then claim the results apply to those other devices.
"The randomized, crossover protocol design consisted of two conditions: (i) reading an LE-eBook (iPad; Apple Inc., Cupertino, CA) in otherwise very dim room light for ∼4 h before bedtime for five consecutive evenings, and (ii) reading printed books in the same very dim room light for ∼4 h before bedtime for five consecutive evenings (Fig. 1)."
This seems like a strange test. When I read a physical book in bed, I need more light (e.g. from a lamp) than when I'm reading on a Kindle or an iPad (which I often read with the lights off, which also means I can turn the backlight to a low setting).
Even stranger is that the iPad was fixed in position on the table, with brightness set to maximum.
The maximum brightness on an iPad means you can read the screen in broad daylight. I can not see how this level of brightness lends itself to bedtime reading in a dimly lit room.
So, they did a user study using iPads, and only measured the other devices. They then claim the results apply to those other devices.
TFA didn't have a link to the paper (as far as I could tell), but it's here: http://www.pnas.org/content/112/4/1232.full?sid=a0e8cb09-0a5...
"The randomized, crossover protocol design consisted of two conditions: (i) reading an LE-eBook (iPad; Apple Inc., Cupertino, CA) in otherwise very dim room light for ∼4 h before bedtime for five consecutive evenings, and (ii) reading printed books in the same very dim room light for ∼4 h before bedtime for five consecutive evenings (Fig. 1)."
This seems like a strange test. When I read a physical book in bed, I need more light (e.g. from a lamp) than when I'm reading on a Kindle or an iPad (which I often read with the lights off, which also means I can turn the backlight to a low setting).