It may make you hungry.

This has nothing to do with the recipes you've been collecting on Pinterest: When people were exposed to light with enriched blue wavelengths—like those in tablets, laptops and smartphones, but stronger—at dinnertime, they reported feeling hungrier than those who ate a same-calorie meal under ordinary dim light. This increase in appetite started about 15 minutes after the light was turned on and lasted for more than two hours. Blood tests showed that the blue light subjects had higher insulin levels as well as higher glucose levels. This may mean that the light makes the body less efficient at metabolizing the evening meal, speculated Ivy N. Cheung, a doctoral candidate in Northwestern University‚Äôs Interdepartmental Neuroscience Program, who led the research. (Yet another reason to not dine by computer light.)

It can keep you up at night...

You've probably heard that all light suppresses the secretion of melatonin, the hormone that regulates your body clock, but blue light has the strongest effect. Experiments have found that 6.5 hours of exposure to blue light (i.e., the amount of screen time you get in a typical work day) suppressed melatonin for about twice as long as green light (another color that's visible in the spectrum), and also shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours). While a short amount of time in front of a blue screen can tinker with your melatonin levels, most research finds that an hour's worth significantly disrupts slumber. So really, turn everything off before you turn in.

...and also during the day.

There are those times when you want to throw off your body clock—like when you're struggling to keep your eyes open at work. Researchers from Brigham and Women's Hospital have found that exposure to blue light during the day directly and immediately improves alertness and performance. Another study, published in the journal PLoS One, showed that daytime doses of blue light can have similar effects as that other wake-up drug, caffeine. Try turning up your screen to maximum brightness while sipping a cup of coffee.

It can bring you up when you're down.

Some research shows that blue light may play a key role in the brain's ability to process emotions. We know that when you look at blue light—from a gadget or from its other big source, the sun—in the morning, when your body and brain are anticipating that kind of light, you feel happier. But it has the opposite affect if we're exposed to it at night. In a series of experiments with hamsters, researchers found that critters who were exposed to blue light during times when they should have been sleeping showed symptoms of depression and apathy, and also had brain changes that have been associated with depression. Remember: Blue light during the day, everything's okay. Blue light at night...don't say we didn't warn you!


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