Is 'Blue Light' Really That Bad for Us?

Laird Harrison


April 23, 2018

Marketers Distort Blue Light Evidence

Blue light will get you if you don't watch out. That's the message from the advertisers of blue-blocking glasses, computer monitors, and apps for cell phones and tablets. Their websites warn of eye strain, retina damage, and insomnia from the widespread use of light-emitting diodes (LEDs) in these devices and in light bulbs.

"Overexposure to blue light could cause all kinds of problems, including dry eyes to digital eye strain, sleep cycle disruption, and even macular degeneration," Lens Crafters warns. "Blue light gives damage to the inner part of your eye," claims the maker of the AceColor app for iPhones.[1] The Vision Council, a consortium of eyewear manufacturers, lists "blue light filter" as a feature of computer glasses that can "prevent the headaches and light sensitivity that people who spend long hours staring at a monitor often experience."[2]

So one recommendation from Frida H. Rångtell, a neuroscientist at Uppsala University in Sweden, might come as a surprise. "Light as bright as possible and quite a bit of blue light in offices will make you more alert and perform better," she says.

Concerns about blue light are not without justification, Rångtell and other blue light researchers say. Multiple studies have shown that too much blue light too late at night can indeed disrupt sleep. And some preliminary research has associated blue light with macular degeneration. But like the scares about dietary fat or household bacteria, these findings have prompted marketing claims that distort the evidence and ignore important nuances—including potential blue light benefits.

The controversy stems largely from the rapid adoption of LEDs, semiconductors that were first engineered to emit blue light in the late 1980s. Inventors combined a short-wavelength blue LED chip with a yellow phosphor, which partially absorbs the monochromatic blue light and re-emits it as white light with a mixed wavelength.[3]

Compared with the incandescent light bulbs that were the standard household light source until recently, LEDs are smaller, more durable, and more efficient. That has made them the most widely used illumination in screens and monitors of all sorts.[3] In one US survey, 90% of adults who responded reported using some type of light-emitting electronic device within the hour before bedtime.[4]

And, increasingly, LEDs are finding their way into room lighting fixtures. Impressed by the energy savings of LEDs, many countries are starting to ban incandescent bulbs. In the United States, LED home lighting mushroomed from fewer than 400,000 installations in 2009 to 202 million in 2016, one of the fastest adoptions of any technology.[3]

"The concern is that they're so widely used that we're impacting our biology in ways that many of us don't think about, but in ways that if we do it over the long term could have potential effects on our health," says Jeanne Duffy, MBA, PhD, a neuroscientist at Brigham and Women's Hospital in Boston, Massachusetts.

While the light LEDs emit appears white, it differs in composition from the light from other bulbs. Both incandescent and fluorescent lights emit light in a dominant wavelength of about 574 nm, while white LEDs emit a dominant wavelength of about 482nm—the blue light range.[3]

Blue Light and Eye Damage

The sudden increase in blue light use has raised two concerns: eye damage and neurologic effects, particularly on sleep.

The crystalline lens of the human eye blocks most ultraviolet radiation between about 300 and 400 nm, but it blocks only about 60% of radiation between 440 and 500 nm, the blue light spectrum.

Researchers have speculated that blue light might trigger oxidative stress, leading to macular degeneration.[5] Blue light has damaged human retina cells in petri dishes[6] as well as retina cells in the living eyes of laboratory mice, rats, and monkeys.[7]

It's hard to study the effects of blue light in living human subjects, though, because outside of laboratory conditions, damage would be expected only over a long period of time. One study compared two groups of people whose natural lenses were replaced by intraocular lenses to treat cataract. People whose lenses blocked blue light had less fundus autofluorescence, a marker for retina damage.

Another study found that geographic atrophy, a type of macular degeneration, progressed more slowly in people with blue-blocking intraocular lenses. But these studies did not control for confounding factors such as the density of the intraocular lenses or the age and genetic backgrounds of the subjects.[8]

Filtering blue light might also affect visual acuity. Here the evidence is mixed. One study found that the blue light-filtering spectacles increased the wearers' ability to tolerate glare and recover from intense light. But in another study in people with early age-related macular degeneration and intraocular lenses, participants were less able to sort blue socks from navy socks while wearing blue light-filtering spectacles than without the spectacles in dim conditions.[8]

Reviewing the evidence on visual acuity and potential retina damage, the authors of a recent review of blue light-filtering intraocular lenses concluded that the evidence was insufficient to recommend for or against them.[8] And in a recent article written for a lay audience, the American Academy of Ophthalmology stated that, "there is no scientific evidence that blue light from digital devices causes damage to your eye."[9]

In 2015, the Advertising Standards Authority of the United Kingdom cautioned Boots Opticians Ltd to stop claiming that, "Many modern gadgets, whether it's a fancy LED TV or your smartphone, as well as sunlight and energy-saving light bulbs, give off a certain kind of blue light that can cause your retinal cells to deteriorate over time."[10]

But the evidence for the effects of blue light on sleep is more compelling. In addition to the familiar rods and cones that receive light for vision, a third class of intrinsically photosensitive retinal ganglion cells (ipRGCs) measure environmental light to influence melatonin secretion, alertness, the pupillary light reflex, and other aspects of sleep regulation.[11]

While rods reach their peak sensitivity at 506 nm (green light) and cones at 555 nm (green-yellow light), ipRGCs are most sensitive to light at about 480nm, precisely the blue light emitted by LEDs. In the natural environment, blue light is most prevalent when the sun is highest in the sky; sensing this shift in color and intensity, ipRGCs help to cause wakefulness by, among things, suppressing melatonin.[11]

In sleep laboratories, researchers have shown that they can make subjects more alert and lucid by exposing them to blue light. They have used bright blue light to treat seasonal affective disorder and other mood disorders. But blue light exposure close to bedtime can delay the circadian rhythm, resulting in overall poorer quality and shorter duration of sleep.[3]

In one study, Duffy and her colleagues randomly assigned 12 healthy young adults to read either a book on an Apple iPad or a conventional paper-and-ink book in an otherwise dim room each night for about 4 hours before bedtime. After five nights, the participants switched to whichever type of book they had not been reading previously. They found that evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness.[12]

The researchers found 55% less melatonin in the participants' blood on the fifth evening of reading on iPads. On their iPad evenings, the participants felt less sleepy than on their conventional book evenings and took 10 minutes longer to fall asleep. During the night, they had less rapid eye movement. And for hours in the morning, they felt sleepier.[12]

"If we have to get up early to go to school or work, using these devices in the evening will shorten our sleep, which has its own negative effects on our mental and physical health," Duffy says. Some research suggests ambient blue room lighting can have similar effects.[13] Disrupting sleep patterns might not only make people sleepier, it could make them more vulnerable to mental illness and affect the way drugs are metabolized, an international team of researchers warned in a recent review.[3]

Blocking Blue Light: Does It Work?

Responding to such concerns, the makers of devices, apps, intraocular lenses, and glasses have introduced mechanisms to reduce the amount of blue light emitted. Do they work? Here, too, the evidence is mixed.

Most of the research has focused on the use of blue light-filtering glasses. In one study, 14 people with insomnia wore either clear glasses or blue-blocking amber-tinted lenses 2 hours before bedtime for seven nights. They then switched glasses for another seven nights. The nights they wore the amber lenses, the patients fell asleep at the same time, but they slept almost a half hour later the mornings after. And they rated their sleep quality as significantly better.[4]

But not all blue blockers are created equal. The ones in the insomnia study blocked about 65% of blue light. Consumer Reports reported that one pair of glasses it tested cut blue light by about a third, another by about half, and a third almost completely.[14]

And not all findings have pointed in the same direction. Researchers at Flinders University in Adelaide, Australia, compared teenagers using devices with dimmer, redder light with those using devices with brighter, bluer light. They found no difference in sleep and only a small effect on cognitive ability.[15] Such conflicting results illustrate the complexity of the mechanisms governing sleep. "It's not only the blue light that can cause these biological effects," says Duffy. "Blue light may be more efficient, but other wavelengths of light can cause them."

The intensity of light also has an effect, she says. Devices like phones and tablets might pose a special problem because people put their faces so close to them, she says. But the context also matters. "If you stay indoors and don't have windows, and you have dim lighting, a light from this device is going to have more of an impact on you than on someone who is a lifeguard and spends 8 hours in the sunshine every day," she says.

Indeed, Rångtell and her colleagues ran a study similar to Duffy's, with subjects reading a book in print or on an illuminated device for 2 hours before bed. But in this study, they exposed the participants to bright light for 6.5 hours before the reading sessions. They found no difference in sleep or melatonin.[16] Duffy likes the idea of new room lighting that can be set to automatically change both wavelength and brightness with the time of day.

Putting the lessons from her research into practice in her own life, Rångtell dims her lights every evening. "I just turn off a lot of lights and just have lamps that allow me to see what I'm doing," she says. She also keeps her phone and computer out of her bedroom and tries to avoid responding to emails or anything else work-related right before bedtime, reasoning that not only the form but also the content of the media she consumes can affect her sleep. "I can definitely feel the effects of technology." So far, she hasn't seen the need for tinted lenses or blue light-dimming apps.

Ari Shechter, PhD, a sleep researcher at Columbia University in New York and first author of the study treating insomnia with amber-tinted glasses, recommends similar measures for people who are not suffering from a sleep disorder. "For people with insomnia or a sleep disruption, to take an extra step could be useful. Is it necessary for everyone to use these lenses? Probably not."


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