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See the Light

YOU’VE HEARD IT BEFORE: GAZE AT YOUR SMARTPHONE OR E-READER TOO long before bed, and the glowing blue light will keep you awake. But new research suggests that too little light during the day can have equally concerning consequences, boosting the risk of obesity, depression, and possibly even disease.


When bright light hits the eye in the morning, it stimulates specialized cells in the retina to tell the brain’s master clock to reset, explains Phyllis Zee, MD, director of the Sleep and Circadian Rhythms Research Program at Northwestern University Feinberg School of Medicine. That stimulation triggers a cascade of processes throughout the body’s organs that dictate everything from appetite and metabolism to blood pressure and alertness.

If that light trigger comes too late in the day,

things go awry. In one 2014 study, Zee found that people who got the bulk of their bright light exposure before noon were significantly leaner than those exposed to the most bright light in the evening. After controlling for other factors, light timing accounted for about a 1.4-pound difference. Later research found that when people were exposed to bright light at night and then ate, they were more insulin-resistant—meaning less glucose, or sugar, made it into their tissues for fuel and more remained in their blood. Over time, this pattern could lead to weight gain or diabetes.


Other studies show that workers with desks near a window are more alert and productive by day and more physically active after work. And they sleep better at night. In contrast, notes Zee, workers who lack well-timed bright light are more susceptible to heart disease, depression, and certain cancers.

“Many Americans are working in dim environments

all day,” says Zee, “and by the time they leave it’s already dark out. It’s a problem.” But an easily solvable one, she says. While one hour or more of morning light is ideal, her research shows that as little as 30 minutes of bright light exposure within three hours of waking can have a measurable impact on your health.

So walk to work, take your coffee break outside, or pull your desk closer to a window if you can.




Light must be 500 lux (a measure of light intensity) or brighter to stimulate positive health changes. Overhead lights in offices hover around only 200 to 300 lux.


A specialized office lamp set at eye level can provide more than 1,000 lux of light.



Studies show blue-hued light (such as fluorescent or LED bulbs), as opposed to green or orange/red light, immediately improves alertness and reaction times.


Three hours before bedtime, dim your lights and switch to longer, reddish-orange wavelength light (such as “soft” or incandescent bulbs), which has less impact on circadian rhythms.

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