Inside the sleep “suites” at the sleep laboratory at Harvard Medical School—the pods where research subjects live during experiments, with electrodes affixed to their bodies—the most glaring feature is the adjustable lighting, which is spread evenly across the paneled ceiling so there are no visible source points or dark areas. Over the years, electric light has become something of a target for Czeisler. When he is on the convention circuit, light is the subject he sermonizes about most.
In the 1990s, he proved that a human being’s biological clock can be reset—your entire bodily rhythm shifted—with exposure to artificial light. He then proved that this applies to blind people as well. “Ordinary room light is only 1% of the intensity of the light outdoors,” he says, “but it has 50% of the resetting ability.” According to him, short-wavelength light is the more insidious influence on your biological clock. These are the beams emitted by your iPad, plasma television, and even eco-conscious lightbulbs. (The old incandescent lightbulbs, according to Czeisler, emit more heat than actual light.) When this short-wavelength light hits the photosensitive retinal ganglion cells in your eye, it halts the release of “sleep-promoting” neurons and “activates arousal-promoting” neurons. It also suppresses the release of melatonin, the brain’s natural chemical for facilitating drowsiness. In our artificially lit world, he says, it’s likely that most of us have shifted our time zones to the point that sleep—the necessary, healthy kind—is increasingly difficult to achieve.
We go to bed late and force ourselves up too early with caffeine, manipulate our time zones, and burden ourselves with enormous sleep debts that would take weeks of vacation to pay back. In terms of public awareness, “we’re in the 1950s with smoking,” Czeisler says. “A few people on the cutting edge are aware”—such as pro sports teams—“but I wouldn’t say society as a whole is adopting it. Nobody has said, when we release the next [light-emitting] tablet, ‘Look at the health and safety consequences!’ No one is viewing light as something that needs to be evaluated. The light sources are getting brighter and worse.”
So he advises you to dim your lights in the evening, and turn off the TV at least an hour or two before bed. If your phone is your alarm clock, buy an alarm clock. “For uninterrupted sleep, keep your phone in a different place,” he says—otherwise you’ll look at it, and it will invariably buzz. If you need to e-mail, he suggests “installing ‘f.lux’ software on your computer, which changes the wavelength of the light on the screen.” I mention that people have had light—lightbulbs, candles—for quite a while, yet have always stayed up past their bedtimes. Isn’t this a little overblown? “When I was growing up, 2–3% of the population slept less than six hours; now it’s 10 times as many,” he says. “We’ve increased by an order of magnitude our per capita light exposure. Take all the people who died on 9/11—twice as many die in motor vehicle crashes every year in the U.S. alone due to sleep deprivation. There are about 60,000 debilitating injuries on the highway [caused by under-slept drivers]. And we’re getting more overweight because we’re sleeping less. As sleep has gone down, waistlines have gone up. When you don’t get enough sleep, your brain goes into starvation mode.”
So, what can we do? “I don’t know the answer,” Czeisler says. “But I don’t think the answer is for the culture to unlearn our modern way of life.” So he recognizes the challenge. “When I was meeting with an NBA team, I started off my talk by mentioning that people are sleeping less today than when I was young. Their star player said, ‘That’s because back then there was less shit to do!’ ”