Although I don't have any scientific data to back up this theory, my own experiences pretty much verify what is described in the above paragraph. Reading a tree-book in bed makes me sleepy...every time...never fails. On the other hand, reading from my Kindle or iPad not only allows me to read much longer before falling asleep, it also guarantees that I'm going to sleep so lightly that I'll be tired when I climb out of bed in the morning. That happens almost every time.Compared with a printed book, a light-emitting e-book decreased sleepiness, reduced REM sleep (often called dream sleep), and substantially suppressed the normal bedtime rise of melatonin, the hormone that regulates the sleep and wake cycle. The e-book users took longer to fall asleep and felt sleepier in the morning.
I figured this out the hard way a long time ago. Anyone else notice the same thing?