Management Professor Russell Johnson and his colleagues, analyzing studies surveying a broad spectrum of U.S. workers, found people who monitored their smartphones for business purposes after 9 p.m. were more tired and were less engaged the following day on the job.
"Smartphones are almost perfectly designed to disrupt sleep," Johnson said. "Because they keep us mentally engaged late into the evening, they make it hard to detach from work so we can relax and fall asleep."
While many smartphone owners think of their devices as a way to increase their productivity of knowledge-based work, they may be doing just the opposite, he said.
The National Sleep Foundation says only 40 percent of Americans get enough sleep on most nights and a commonly cited reason is smartphone usage for work.
In addition to keeping people mentally engaged at night, smartphone screens emit "blue light" that seems to be the most disruptive of all colors of light on human sleep patterns, Johnson said.
"So it can be a double-edged sword," he said. "The nighttime use of smartphones appears to have both psychological and physiological effects on people's ability to sleep and on sleep's essential recovery functions."
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