[QuantumIguana]

The gold standard of testing is the double-blind test. Of course, that's not possible here, because whether you are reading from paper or a screen is obvious. Still, as many differences as possible should be eliminated. One that stands out was "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." This difference could have easily been eliminated by not allowing either group to hold the book or device.

You can have a real-world test or a more narrowly focused test, but you cannot draw a broad conclusion like "Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness" from a very narrow test. It would be like testing automobile safety only at very high speeds and drawing broad conclusions about automobile safety. The brightness issue is not easily glossed over. If the frequency of the light is a problem, less light should have more of an effect, and conversely, more light should have more of an effect. In dim light, people lower the brightness of their devices. On the Kindle Fire, I can switch to white letters on a black screen, and thus use considerably less light. I find it quite uncomfortable to have the brightness at full in dim light. It may be true that other devices are brighter, but if people don't use their devices at full brightness in dim light, it is irrelevant that there are devices that could be even brighter. If they tested at lower levels of brightness and let people read the devices as they wished, if the effect persisted, their conclusion would be much stronger. As it is, it isn't worth all that much. A more reasonable conclusion might have been "Evening use of light-emitting eReaders at high levels of brightness negatively affects sleep, circadian timing, and next-morning alertness"