The New Yorker had a three part article on sleep.
- Why Can’t We Fall Asleep? - falling asleep
- The Work We Do While We Sleep - sleeping and dreaming
- The Walking Dead - wakefulness
Here's a bit from part one:
But it may be that the most important aspect of sleep hygiene has to do with light—which, of course, has gotten more pervasive during the past century, especially at night. Humans have evolved to be exquisitely sensitive to the most minute changes in the light around us. In fact, there are specific photoreceptors in the eye that only respond to changes in light and dark, and which are used almost exclusively to regulate our circadian rhythms. These melanopsin receptors connect directly to the part of the brain that regulates our internal body clocks. They work even in many people who are blind: though they can’t see anything else, their bodies still know how to adjust their circadian clocks to stay on schedule. Light helps the body predict the future: it’s a sign of how our environment will change in the coming hours and days, and our bodies prepare themselves accordingly. As the Harvard circadian neuroscientist Steven Lockley told me, “Our clocks have evolved to anticipate tomorrow.”
Now, however, that natural prediction system is being constantly wrong-footed. The problem isn’t just artificial light in general. Increasingly, we are surrounded by light on the short-wave, or “blue light,” spectrum—light which our circadian systems interpret as daylight. Blue light emanates from our computers, our televisions, our phones, and our e-readers; ninety per cent of Americans use electronic devices that emit it. When we spend time with a blue-light-emitting device, we are, in essence, postponing the signal to our brain that tells it that it’s time to go to sleep. (“What have we done with our dusk?” Charles Czeisler asks.) When “dusk” gets pushed progressively later because of these false light cues, we get a surge of energy rather than the intended melatonin release.
Czeisler has found that artificial light can shift our internal clocks by four or even six time zones, depending on when we’re exposed to it. In one study, out earlier this year in the journal PNAS, Czeisler and his colleagues asked people to read either a printed book or a light-emitting e-book about four hours before bed, for five evenings in a row. The effects were profound. Those who’d read an e-book released less melatonin and were less sleepy than those who’d read a regular book; their melatonin release was delayed by more than an hour and a half, and their circadian clocks were time-shifted. It took them longer to fall asleep. The next morning, they were less alert. These resetting effects can result not just from prolonged reading but from a single exposure. In his sleep lab, Lockley has seen it happen after exposing subjects to short-wavelength light for less than twelve minutes.
As a result of this I installed f.lux on my iMac (I'd heard of it before and was already interested and it works on all platforms) and read a physical book last night (John Cleese's autobiography So Anyway...). FYI, Flux "makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day."