How Much Light Do You Really Need While Reading?

“Turn on a light! You’ll ruin your eyes! ” I grew up with warnings like these, followed by the click of a light switches, almost every time my mother found me nose-deep in a book. She never listened to my arguments that I could see the pages just fine. The Mom Logic was straightforward and unyielding: If I didn’t turn on more lights, I’d harm my eyes and potentially lose my greatest pleasure in life, my ability to read.

The Mom Logic was also wrong, though it’s a myth with a lot of mileage. In 1604, no less an expert than Dutch astronomer and “founder of modern optics” Johannes Kepler blamed the amount of time he spent studying for his nearsightedness. It’s not a big leap from there to the assumption that inadequate light while reading can make the situation worse (though one doctor hypothesizes that parents have mainly used the threat to get their children to go to sleep).

However the myth that reading in dim light is harmful got started, it’s simply not true. So says Dr. Sunir J. Garg, clinical spokesperson for the American Academy of Ophthalmology (AAO) and professor of ophthalmology at Wills Eye Hospital in Philadelphia, who assures us there is no scientific evidence to suggests reading in dim light does any damage to your eyesight or the health of your eye at all.

“It’s not a safety issue, [so much] as it is a personal comfort kind of an issue,” Dr. Garg tells me. In his own home, in fact, his wife reads at night using just her backlit ereader or the focused beam of a desk lamp. (He prefers the consistency of overhead lights.)

Our eyes are far hardier than their squishiness (flashback to that scene in Kill Bill: Vol. 2) might suggest, though vision problems are nothing to squint at. Read on—using whatever amount of light you desire—to learn more.

Reading “in the dark” does not harm your eyes, period

One way to stop someone repeating the reading in the dark myth in their tracks is to ask them exactly how a lack of light could even harm the eyes. It’s not as if people’s eyes start melting like scoops of ice cream when they’re reading in a dim room, or that blindness will suddenly descend mid-book (just when you were getting to the good part, probably).

Usually, the person warning you is implying that repeated reading in low light can, over time, cause refractive errors: the medical term for vision problems. There are four main types of refractive errors:myopia(nearsightedness), hyperopia (farsightedness), astigmatism (general blurriness caused by the cornea and lens changing shape), and presbyopia (age-related issues seeing up close that usually require reading glasses). All of these issues stem from changes in the shape of the eye that prevent the light coming in from focusing on the back of the retina. Three-quarters of these conditions have to do with difficulty seeing things up close: the kind of vision problem you’re going to notice most when reading.

Nearsightedness is by far the most common vision problem worldwide. It’s also been rising at a shocking rate since the second half of the 20th century. Studies estimate that over half the global population could have some degree of nearsightedness by 2050. In the U.S., nearsightedness increased from 25 percent of the population in 1971 to around 40 percent today, with a 14 percent increase from 2000 alone. The condition has particularly skyrocketed in East Asia, however, where China, Japan, Singapore, South Korea, and Taiwan have rates of myopia as high as 80-90 percent of children and adolescents (up from just 10-20 percent in certain areas in the 1950s.)

Some of this rise could be due to greater awareness of, and access to, eye exams and glasses in developing nations, especially for kids between the ages of 6 to 12, when many people first develop a need for corrective lenses. Even factoring in that possibility, however, the rate of increase is simply too high for genetics— which emerged as the primary culprit in the 1960s and 70s—to be the sole cause.

Heredity remains one of the most important predictors of nearsightedness, with studies identifying over 100 genetic markers linked to the condition. Yet scientists acknowledge that children inherit not only genes but also lifestyles from their parents, and some studies posit that the number of hours spent studying (or rereading Harry Potter) increases the risk of developing myopia, especially during elementary and middle school.

Still, none of these studies has found any particular link between nearsightedness and the amount of light used when doing so-called near work like reading, even at night. “From an eye health perspective, as far as we know, it doesn’t seem to matter,” Dr. Garg says. “It really boils down to whatever works for you and is most comfortable.”

There’s no such thing as too much light—even blue light

When I read in bed, the desk lamp on my nightstand is parallel to my eyes, so the light often shines into, rather than above, them. When I ask Dr. Garg about this, he tells me not to worry; my eyes can handle those beams just fine.

But what if the direct light is blue light from an ereader, tablet, or smartphone? “There’s very little to no high quality scientific data to suggest that blue light from our screens poses any problem to us,” he says. Blue light does affect our circadian rhythms, it’s true—though it’s worth noting that one of the most commonly cited studies found that participants exposed to blue light at night fell asleep, on average, only 10 minutes later than the control group. (Other scientists argue that the study’s lab conditions grossly underestimated the amount of natural and artificial light most people experience in a 24-hour period, a factor that might have exaggerated the results.)

“People have been exposed to blue light for thousands or tens of thousands of years,” Dr. Garg points out, “because blue light is part of sunlight.”

He goes on: “We get exposed to way more blue light on a regular outdoor working day than we ever would by looking at our screen for eight hours a day.” A sunny afternoon is, after all, a whopping 100,000 times brighter than our computer screens.

That means using dark mode or nighttime settings on your screens won’t do any harm, but it probably won’t do much good, either. And don’t waste your money on those blue-light blocking glasses unless you like spending money on things that don’t work. No judgment!

You especially want to avoid blue light filtering glasses when you’re outside, because one of the more intriguing hypotheses about the rise in myopia worldwide has to do with a lack of exposure to outdoor light. Multiple studies have shown that children who spend more time outdoors develop less myopia. It’s not yet clear why this is, though two possible explanations are the relative brightness of sunlight compared to indoor light and the fact that close-up work more often takes place indoors. Some scientists even insist that exposure to light itself may not be the real benefit of time outdoors, but some other factor. That hasn’t stopped some nations like Taiwan from instituting mandatory time outdoors for younger children; one study found that nearsightedness in 5-6 year-olds in a Taiwanese city declined by almost 50 percent two years after the initiative was adopted.

That said, this is a good time to remind you to wear UV-blocking sunglasses and not to stare directly at the sun when you do emerge from your wifi-equipped cave. Doing the latter for just a few seconds can cause temporary damage, while about 100 seconds of sun-staring can lead to permanent damage; symptoms range from light sensitivity, pain, blurred vision, and even blindness. Wearing UV-blocking sunglasses outside is as essential as putting on sunscreen.

Reading in any kind of light can cause discomfort, but not damage

No matter what kind of light you use, long periods of near work will inevitably cause eye strain—the catch-all term for a variety of symptoms you might experience when you overwork your eyes. These symptoms include:

One of the prime causes of eye strain is blinking less, which happens whenever we focus on something. “If you look at a little kid playing a video game, they don’t blink,” says Dr. Garg. “Physically, a similar thing happens to adults.”

Blinking wets the eyes with tears that contain nutrients and oxygen needed to keep the eye healthy. We typically blink anywhere from 12 to 15 times per minute, but that rate can drop as much as 60 percent when using a computer. Reading a book can be even worse.

At the same time we’re not blinking, we’re also wearing out our eyes by locking them in the same position for a long period of time. Dr. Garg compares it to holding out your arm or standing in the same position for long periods of time.

As uncomfortable as this dryness and fatigue sound, they are temporary discomforts with relatively easy solutions and no permanent consequences. Dr. Garg says repetitive eye strain, unlike repetitive strain of the limbs, does not lead to cumulative or permanent damage. Moreover, not everyone experiences eye strain; it varies from person to person and can get better or worse (usually the latter) as we age.

If your eyes start to feel sandblasted after a couple of hours, there are two things you can do: moisturize your eyes, and give them a break. To lubricate your eyes, start with artificial tears or rewetting drops. Any brand will do, though contact lens wearers should use rewetting drops specifically for lenses, as other types may cloud your vision.

If you live in a particularly dry environment, you might also consider a humidifier. Again, this has to do with personal preference and individual experience more than necessity. Dr. Garg, for instance, finds that the dry winters in Philadelphia and central heating crack his skin and parch his eyes, so he uses humidifiers at home.

To give your eyes a break, follow the 20-20-20 rule: every 20 minutes, look at an object at least 20 feet away for at least 20 seconds. It’s the eye equivalent of getting up to stroll around the office and stretch your muscles to mitigate the ills of sedentary work. Plus, it gives the eye muscles a chance to switch from the slightly cross-eyed position they fall into when doing near work. (Another myth to bust here:: Your eyes will not get stuck if you cross them.)

If you find your quality of life and time at work affected by dry eye in particular, Dr. Garg recommends you consult with an eye doctor. “What we’re able to do now...is substantially better than it was even five years ago,” he says.

The best way to take care of your eyes is to take care of your body

One of the ironic things about eye health is that we feel the discomfort of eye strain more easily than we do many severe and permanent eye diseases like macular degeneration, glaucoma, and diabetic retinopathy. “There’s not a lot of pain for a number of eye diseases, and some of them don’t even cause vision loss until they’re fairly far along,” says Dr. Garg.

Screening recommendations are all over the place when it comes to the eyes, in part because people with corrective lenses usually need more frequent visits than someone with 20/20 vision, mainly because they need their prescriptions checked and changed regularly. The AAO recommends that adults who have neither symptoms nor risk factors for eye diseases get a baseline examination at 40, whereas the American Optometric Association (AOA) recommends annual exams for all adults 18 and over who have risk factors and at least every two years for adults aged 18-64. Risk factors include:

As important as regular vision screenings are, however, one of the best things you can do for your eyes is to follow general health guidelines. “Things that are good for your whole body are great for your eyes,” Dr. Garg says.

So, don’t smoke. (Or quit if you do.) Eat at least three servings of leafy green vegetables and foods high in omega-3 fatty acids (especially fish) per week. Fit in about 30 minutes of moderate cardiovascular exercise (e.g., a brisk walk) three times a week. “For most people, that’s all that they need to do for general eye health,” Dr. Garg maintains.

And don’t worry about the amount of light you use when reading—unless you need a rebuttal to the hypochondriac in your family. Then, by all means, show them this piece.

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