Does reading in dim light really hurt your eyes?

boy and girl read by flashlight under the covers
Young readers and their trusty flashlights
Alistair Berg/Digital Vision/Getty Images

There are many nights in a young child's life when bedtime comes far too early. Sleep seems like a distant possibility, yet parents insist that the child remain in bed with the lights off. In this situation, many children have resorted to reading under their covers by flashlight. The meager beams of light ensure that parental attention won't be aroused while providing the children with a chance to catch up with their favorite fictional characters, from girl detectives to boy wizards and talking animals.

Unfortunately, children engaging in this activity have frequently been caught by their snooping parents. And not only is there a potential punishment in store for staying up past lights out, children are also issued the ominous warning that their dimly lit reading will ruin their eyes. This scenario may represent one of the few times in which children aren't praised for their diligent reading habits.


Yet if these children are avid readers who've consumed a few tales of pioneer life, they may wonder if this threat holds true. After all, generations of people had only candlelight to read by, and they turned out just fine. Are today's parents just overprotective of our eyesight?

As it turns out, they probably are, but they're not the only ones. In 2007, the idea that reading in dim light ruins eyesight was named one of the seven medical myths that doctors are most likely to believe [source: Parker-Pope]. The study, published in the British Medical Journal, revealed that reading in low light does not damage eyes, but rather causes eye strain. Eye strain is no walk in the park, though. Find out more about this phenomenon on the next page.


Eye Strain and Reading in Dim Light

woman reading with lamp
Though reading in dim light won't ruin your eyes, you'll be more comfortable with a good lamp.
Matt Gray/Digital Vision/Getty Images

When you walk into a room where light is low, your eye adjusts in several ways. First, the rod and cone cells on the retina begin to produce more light-sensitive chemicals. These chemicals detect light, convert it to an electrical signal and transmit that signal to the brain. Second, the iris muscles relax, which causes the opening of your eye, the pupil, to become very large. This allows your eye to collect as much light as possible. Finally, the nerve cells in the retina adapt so that they can work in low light. When you read, your eye must be able to focus an image of the words onto your retina. To do this, the iris, as well as the muscles that control the shape of your lens, must contract to keep the focused image on the retina.

If you read in low light, your visual muscles get mixed signals: Relax to collect the most light, but at the same time, contract to maintain the focused image. When that object is poorly lit, focusing becomes even more difficult because the contrast between the words and the page isn't as great, which decreases the eye's ability to distinguish visual detail. That ability is called visual acuity. Your eyes have to work harder to separate the words from the page, which strains your eye muscles.


When your eyes are working this hard for a long period of time, they become tired, much as any muscle would. The strain may result in a number of physical effects including sore or itching eyeballs, headaches, back and neck aches and blurred vision. Because you often don't blink enough when focusing on a single object, you may also experience uncomfortable dryness in your eyes. None of these symptoms damage your eyes, and they eventually go away. If the symptoms don't go away once you stop straining your eyes, however, then see an eye doctor. You may have an underlying eye problem like nearsightedness; the fact that the symptoms of eye strain overlap with those of nearsightedness is likely a reason why some continue to argue that reading in dim light causes permanent damage.

For now, it seems, the eyesight of children who read by flashlight is safe. Still, it's certainly easier on your eyes to read in good light that falls directly on the page without causing a glare. You can also avoid eye strain when you're reading by blinking frequently and taking a moment to focus on something out the window or across the room every 15 to 30 minutes.


Lots More Information

Related HowStuffWorks Articles

  • Bianco, Carl. "How Vision Works." HowStuffWorks. April 1, 2000. (July 15, 2009)
  • "Eyestrain." Mayo Clinic. July 12, 2008. (July 12, 2009)
  • "From Light to Vision: Anatomy of the Eye." Pendleton Eye Center. April 5, 2001. (July 15, 2009)
  • "How to Prevent Eye Problems." Consumer Reports on Health. March 2006.
  • Parker-Pope, Tara. "Medical Myths Even Doctors Believe." New York Times. Dec. 26, 2007. (July 12, 2009)
  • Ray, C. Claiborne. "Q&A." New York Times. Aug. 13, 1991. (July 12, 2009)
  • Ray, C. Claiborne. "Q&A." New York Times. June 2, 1998. (July 12, 2009)
  • Vreeman, Rachel C. and Aaron E. Carroll. "Medical Myths." British Medical Journal. December 2007. (July 12, 2009)