> The light emitted by most e-readers is shining directly into the eyes of the reader, whereas from a printed book or the original Kindle, the reader is only exposed to reflected light from the pages of the book.
So it's talking entirely about brightly backlit tablets, not e-readers with e-ink.
Also, I dispute the OP's contention that reflected light on s paper book is any better; certainly, a normal bed-side lamp is worse for the sleep of anyone sharing the room with the reader.
EDIT. Although like I just said, an iPad probably has less of a deleterious effect on sleep than a Kindle Paperwhite does, it is probably possible to do better in the current market. Specifically, Samsung makes a tablet (the Tab S, which comes in 10.5- and 8.4-inch versions) with an OLED display, which has the advantage over LCD displays that the portions of the screen that are supposed to be black do not emit any light at all. Especially if used with software that displays red or orange text on a black background (to minimize the blue-ish photons) an OLED display is the best choice in the current smartphone-plus-tablet market AFAICT if protection of sleep is the main consideration.
EDIT. Oops, I forgot to include my main reason for preferring the iPad to the Paperwhite: on iOS, Settings > Accessibility > Invert Colors reverses black and white. Combined with the fact that many iOS apps like Safari and iBooks normally present a white field broken only by text and thin lines, the use of "Invert colors" probably results in less light entering the eye than a Paperwhite since (unless they changed it since I last updated the software on my Paperwithe a couple of months ago) you cannot alter the Paperwhite's default color scheme of black text on a white background. I will concede that the Paperwhite's brightness setting goes a lot dimmer than the iPad's does, but I consider that consideration to be trumped by what I just wrote, and, again, neither Paperwhite nor iPad comes close IMHO to an OLED display used with decent software.
The LEDs in the Paperwhite Kindles do not shine light directly in the eyes: the leds shine from below the screen towards the top end of the screen. As it exits the LEDs, light is reflected inside a light guide from which it exits towards the display from specific holes, much like a leaky fiberoptic cable[1].
The directionality and position of the LEDs, and the existence of the light guide, are precisely the differences which make the Paperwhite unlike a backlit display.
[1] http://www.nytimes.com/interactive/2012/12/26/technology/lig...
For the sake of simplicity and to keep it as thin as possible, they use edge-LED lighting with a diffusor layer to spread the light evenly.
Kindle Paperwhite however has 100% reflective e-ink screen plus set of LCDs that shine through the light guide layer above the screen. Some people think that makes it better than transmissive LCDs - that's why using Kindle Paperwhite instead of iPad in this test would be much more insightful, as sleep-disturbing properties of transmissive, blue-tinted LCDs are nothing that wasn't known before.
For reference for those who don't have a Paper White; when at its dimmest setting, it is probably less than the ambient light in the room from neighbors porch lights and street lights. It is almost completely dark, and looks like an older non-lit Kindle in any room with lights on. I do wish it could turn off completely, however.
You can "jailbreak" it and simply control it via standard LED sysfs interface.
uh, how so? You didn't give an argument for this point. At the very least Kindles go far dimmer than iPads do.
(Kindle paperwhite owner and frequent iPad user here.)
What is it about the photons entering the eye that you imagine makes the "frontlit" display of the Paperwhite better than a backlit LCD display?
Check out the "light guide" description here:
http://www.nytimes.com/interactive/2012/12/26/technology/lig...
It's a matter of intensity and spectrum, not if it's reflected or not.