Having trouble getting to sleep? It could be your iPad, your Kindle or any other screen you use for reading before turning the lights out. New research explains why this happens, but what can you do about it — short of giving up your device?

The Lighting Research Center at the Rensselaer Polytechnic Institute recently published a study that explained how readers's beloved tablets and e-readers keep users up at night. A dark room triggers the body's production of melatonin, a hormone that acts as a messenger telling the body it's time to sleep, and lighted screens interfere with that message.

Any light can make it tough to fall asleep (that's why many parents with young children bemoan the onset of daylight savings time), but light of shorter wavelengths, such as the bluish tints emitted from an LED-backlit screens, suppresses nocturnal melatonin, according to the sleep study. The brighter the light and longer the exposure, the more difficulty it will cause in falling asleep.

The findings come just after Amazon introduced its new Kindle Paperwhite e-readers, which offer higher contrast, lit displays, an answer to Barnes & Nobles' popular Nook with GlowLight. And multi-purpose tablets such as the iPad and newcomer Google Nexus 7 are frequently used as e-book readers. But new features aren't necessarily better when it comes to sleep.

[How Amazon's Kindle Paperwhite Technology Works ]


"The ones that do not emit light should be better [for sleeping]," Mariana Figueiro, director of the Lighting Research Center's Light and Health Program, told TechNewsDaily.

She offered some tips for getting a better night's sleep without giving up your e-reader or tablet.

Figueiro recommends reducing the brightness of the screen to its minimum (which helps conserve battery life, too). Tablet users can go into "settings" to do this. Kindles and Nooks that lack a built-in light cannot adjust the screen, but because the device's e-ink displays have lower contrast, these e-readers are less disruptive to sleep. However, Kindle Paperwhites and Nook with GlowLight should be dimmed as much as possible.

Readers should also reduce the amount of time spent using the device prior to bedtime.

"One hour exposure is not as bad. After two hours, we saw significant melatonin suppression," Figueiro said. "Power it off at least one hour prior to bed."

Most devices give users some text and display color options for reading. For instance, in iBooks for the iPad, tapping the font icon at the top right corner of a page displays a number of adjustments for nighttime reading. Here, readers can dim the screen and choose the Night theme, which shows white type on a black field, the configuration Figueiro recommended. E-readers and Kindle or Nook apps used on a laptop or other device offer the same white-on-black scheme.

Despite what your mom probably told you as a kid ("Read in bright light or you'll go blind"), reading in lower light isn't harmful, and it will make falling asleep easier.

"Low level illumination, equivalent to a nightlight, for example, is okay with a tablet," Figueiro said. You should also hold your device as far away from your eyes as possible — and comfortable — to reduce the amount of light that reaches the eyes. Enlarge the font size if necessary, a feature that all e-readers, tablets and reading apps offer.

If you're still having trouble falling asleep, it may not be your device.

"All of these will help minimize melatonin suppression, but one can still be active and alert because of the task," she said. "So we cannot blame it all on the light coming from the screen."

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