Raise your hand if you’ve ever stayed up late reading emails, catching up on Facebook, tweeting, texting, or watching movies. You’re not alone. You might even be among the millions of Americans who bring their tablets, e-readers, smartphones, and laptops with them to bed each night.
Sleep experts, of course, recommend turning off our devices a couple hours before bedtime. This is partly to allow time for our over-stimulated minds to wind down. But there’s an even more important reason: The LED screens on our devices produce an abundant amount of blue light, and this particular light is wreaking havoc with our sleep and our health.
Blue light is a component of visible light occurring at the short wavelength end of the visible spectrum. During the day, blue light makes us alert and boosts our mood. But when we’re exposed to too much blue light in the evening, our bodies suppress production of the hormone melatonin. In the evening, melatonin is supposed to increase, helping us to sleep, signaling our bodies to begin important nighttime processes, and keeping us in sync with our natural circadian — or daily — rhythms.
What happens when circadian rhythms get knocked out of whack? Quite a bit. Disruption of melatonin and circadian rhythms has been linked in numerous studies to an increase in heart disease, depression, diabetes, obesity, and both prostate and breast cancers. Researchers aren’t sure exactly why this is, but they do know that people whose circadian rhythms and melatonin are most strongly disrupted, such as night-shift workers, have higher than normal incidences of these diseases.
When Harvard researchers tested a group of subjects by altering their schedules and, therefore, their circadian rhythms, the subjects’ blood sugar increased, and their levels of the hormone leptin went down. Leptin helps us feel full after a meal and signals us to stop eating. This may explain why suppression of melatonin is linked with diabetes and obesity.
Though all visible light is capable of suppressing melatonin, the red end of the spectrum suppresses it the least, and the blue end the most. Because of the way LED screens are designed, the light emitted from them — even white light — contains a high amount of the blue wavelength.
What does this mean for those of us who use our electronic devices in the evening, often after we’re in bed? Researchers at Rensselaer Polytechnic Institute recently provided an estimate when its Lighting Research Center published a study showing that two hours of exposure to an electronic device with a self-luminous (back-lit) display can suppress melatonin production by 22 percent.
The amount of blue light actually reaching your eyes can vary, though, depending on the particular device, the duration of exposure, distance from the device to our eyes, and what you’re actually doing when you’re using it. Illuminance can vary from a dim five lux to a bright 50 lux. (To put this into perspective, a night light puts out about four lux.)
If you suffer from insomnia, you’d be wise to avoid LED screens for a couple hours before bedtime. But what if you like to relax before sleep by playing Words With Friends, reading a book on your Kindle, or streaming a sitcom on your iPad? Until manufacturers develop melatonin-friendly screens (which some are purportedly working on) here are ways to minimize your exposure to blue light:
1. Use your devices for an hour or less in the evening. The Rensselaer study found that an hour of exposure didn’t significantly alter melatonin production.
2. Dim the screen if possible.
3. Watch movies on your TV rather than on a laptop or tablet. We sit farther from a TV, so less blue light reaches our eyes.
4. If reading text, switch to white on black.
5. Download f.lux, a free program from stereopsis.com/flux that adjusts the brightness of your screen depending on the time of day. It removes up to three-quarters of the blue light and can be customized and instantly adjusted.
6. Choose clock radios with displays in green or red instead of blue.
7. Many control panels and power buttons on appliances, stereos, etc., are a single wavelength of intense blue, and often brighter than a night-light. The rods in our eyes perceive blue to be brighter at night, so cover these display lights with tape.
8. Sleep in complete darkness. If you need a nightlight, choose one with a red or orange bulb.
9. Use incandescent bulbs in your bedside lamp, especially if you use that lamp for reading before bed. Unfortunately, energy-efficient LED and fluorescent bulbs (including swirly CFLs) produce more blue light than incandescents.
10. A couple hours before bedtime, dim the lights around your home. Use accent lighting instead of bright overhead lights.
11. If you work the swing or night shift (especially if your workplace uses fluorescent lights or if you’re at a computer for much of the time), consider wearing glasses that block blue light. These can be made for prescription lenses, too.
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