[IRP]

Leds in a phone or tablet screen are directing the light to your eyes, where with a backlit screen, that light is diffused over the area of the screen. So the intensity of direct light from "LE-eReaders" is probably way higher than that of a backlit screen.

Also, it might have to see with the level of blue light that is emitted by those devices. Light in backlit screens is somewhat filtered and might not contain as much blue.

[nicoburns]

> Also, it might have to see with the level of blue light that is emitted by those devices

In my experience backlit screens contain a lot of blue. I have been able remove the waking effect of my screen entirely using a heavy red filter provided by f.lux. But with the default settings, and even Apple's night shift implementation it's very blue. It is slightly less bad on newer devices that support "TrueTone".

[Karawebnetwork]

Elsewhere I would agree with you but this study was using:

"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"

In other words, they compared using a tablet to reading a book. Unsurprisingly, they found that using the tablet negatively affects sleep.

[manicdee]

During LE-eBook reading sessions, the light-emitting device was set to maximum brightness and placed in a stand that held it at a fixed angle. This stand was placed on a table directly in front of the individual at a 30- to 45-cm distance from their eyes. Participants were allowed to turn pages on the LE-eBook, but were asked not to hold it while reading or make any adjustments to the settings. During the printed book reading sessions, participants were allowed to hold the book at any desired distance from their eyes.

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Note that maximum brightness on an iPad is intended for reading in direct sunlight.