In the early days of the light bulb, Thomas Edison assured people his invention wouldn’t harm health or disrupt sleep.

But as we increasingly migrate toward a 24/7 plugged-in society, Harvard sleep expert Charles Czeisler casts doubt on that assurance.

“The more we light up our lives, the less we seem to sleep,” Czeisler wrote in a commentary in the journal Nature. “As the cost of generating light has plummeted by two orders of magnitude over the past century, its consumption has increased accordingly. Between 1950 and 2000, for example, as the cost of light production fell sixfold, UK per capita light consumption rose fourfold. This increasing light consumption has paralleled the rise in sleep deficiency.”

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Does that mean you should pick up a book made of paper before sunset, instead of downloading a novel to your tablet after dark? Ideally, yes.

“Technology has effectively decoupled us from the natural 24-hour day to which our bodies evolved, driving us to go to bed later,” Czeisler wrote. “And we use caffeine in the morning to rise as early as we ever did, putting the squeeze on sleep.”

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Between 50 and 70 million Americans experience health and safety issues from sleep disorders and sleep deficiency, according to an estimate by the U.S. Institute of Medicine.

But while technology is part of the problem, it could also be part of the solution. LED lights usually emit mostly blue light, which is more disruptive to circadian rhythms and melatonin secretion, according to Czeisler. But it would be easy enough to change them to emit more red- or orange-enriched white light after sunset, he said, which could re-attune bodies to the natural rhythm of the day.

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