Does blue light really keep you awake?

The link between blue light and sleep is murkier than people think

- Caroline Hopkins Legaspi

NEW YORK - Experts have long warned about the dangers of blue light before bed. When exposed via smartphones, TVs, laptops and other devices, your brain suppresses the production of the hormone melatonin, which normally makes you feel drowsy. As a result, you feel more alert, making it harder to fall asleep.

But the link between blue light and sleep is murkier than people think, said Dr. Lauren E. Hartstein, an assistant professor of psychiatry at the University of Arizona. She and other researchers have been taking a closer look at the evidence, which suggests that blue light alone may not be causing poor sleep. In some cases, screen use could even help you drift off.

Here is what studies on blue light suggest and what may help you sleep more soundly.

RESEARCH ON BLUE LIGHT AND SLEEP IS MIXED

Many of the available studies on blue light and sleep are old and limited by their small sample sizes. They were also often performed in carefully controlled laboratories, so their results do not always reflect real life, Dr. Hartstein said.

While it is true that blue-light exposure can sink melatonin levels, the limited evidence suggests that screen use does not always cause this dip, said Dr. Mariana Figueiro, a scientist at the Icahn School of Medicine at Mount Sinai in New York City who studies how light influences health.

Some of her research suggests, for instance, that how long you use your device for, how close it is to your eyes and how bright it is may play a role. One of her studies from 2013 found that using a tablet at full brightness for two hours caused melatonin levels to drop slightly, whereas using it for one hour caused no change.