Sleeping with the light on and your child's eyes: what the studies found

If your child sleeps with a lamp or a night light on, you may have read that it causes short-sightedness. The claim is more than twenty-five years old, it came from a respected journal, and it has never quite gone away. So it deserves a proper answer, not a shrug. Here is what the original report did and did not show, what the studies that followed found, and what the evidence now says does make a difference.

The short version is that the link did not hold up. Short-sightedness (myopia, where distant things are blurred) is real and rising, but a light left on in a bedroom is not a cause that the later research supports.

Does sleeping with the light on cause short-sightedness in children?

Not on the evidence we have. A 1999 report found an association, but two studies published a year later could not confirm it, and a 2001 study of schoolchildren in Singapore found no difference either. The most likely reason for the early result is that short-sighted parents tend to leave lights on, and short-sightedness runs in families. The rest of this page goes through each study so that you can see why.

What did the 1999 report in Nature actually find?

It found that children who had slept with more light in their room before the age of two were more likely to be short-sighted when they were older. The paper is by Quinn, Shin, Maguire and Stone, from the Children's Hospital of Philadelphia and the University of Pennsylvania, and it appeared in Nature in May 1999. Its summary reports a strong association between short-sightedness and light exposure during sleep, at night, in children before they reached two years of age.

The numbers, as reported in the University of Pennsylvania's press release, came from parent questionnaires about 479 children. Of those who slept in the dark before age 2, 10% were short-sighted. Of those with a night light, 34% were. Of those with a room light on, 55% were. That is a large gap, and it is why the finding spread so widely.

What the study was, matters as much as what it found. It asked parents to recall, years later, what the bedroom lighting had been. It was not a trial in which lighting was assigned. As the follow-up authors later pointed out, it had no information on the parents' own eyesight, and its children were drawn from a hospital eye clinic, not from the general population. Dr Richard Stone, one of the authors, said in the press release that the study does not establish that night-time lighting in early childhood is a direct cause of myopia, and that there are undoubtedly other risk factors. That sentence rarely travelled with the headline.

Why did two studies the next year find something different?

Because they asked the same question of other children and also asked about the parents' eyes. Both appeared in Nature on 9 March 2000, and neither could confirm the 1999 result.

The first, from Zadnik and colleagues at Ohio State University, used 1,220 children from a large multi-centre study, with a median age of 10.2 years. Their eyes were measured with drops that relax focusing, which gives a more reliable reading in children. Of 417 children who slept in darkness, 84 (20.0%) were short-sighted. Of 758 who slept with a night light before age two, 128 (16.8%) were. Of 45 who slept with full room lights, 10 (22.2%) were. The authors called the spread remarkably uniform. They also found that parents who were themselves short-sighted were more likely to have used night-time lighting.

The second, from Gwiazda and colleagues at the New England College of Optometry, used 213 children and their parents, aged 2 to 24 years. Twenty per cent of those who had slept with a night light before age two were short-sighted, the same as those who had slept in the dark. They too found that families with two short-sighted parents reported using ambient lighting at night more often.

Put the two findings together and you get the likely explanation. Short-sighted parents leave a light on, perhaps because they cannot see well at night, and short-sighted parents are more likely to have short-sighted children, because the condition runs in families. The light and the short-sightedness then travel together without one causing the other. Statisticians call this confounding.

The Philadelphia team replied in the same issue, and fairly. They pointed out that the families in the other studies were different: their own children were younger, with more short-sightedness, from a hospital clinic. They said that shared habits such as night lighting cannot be ruled out in advance as part of a family pattern, and they raised the possibility that parents of short-sighted children might under-report a habit they feared had harmed their child. They said it remained to be determined whether a lack of daily darkness in infancy speeds up short-sightedness in some children who are already predisposed. What the 2000 reports did show is that the strong association did not appear in two other groups of children.

Does this hold in Asian children, where short-sightedness is commoner?

A study from Asia that could be checked for this page found no link either. In 2001 Saw and colleagues published a cross-sectional study of 1,001 children in two Singapore schools, with eye measurements taken after drops and parent questionnaires on lighting, near work and family background. Myopia was found in 33.1% of children who had slept with a light on before age 2 and in 31.4% of children who slept in the dark, and the length of the eye was not related to night lighting. The result held after allowing for near work, and the authors concluded that myopia is not associated with night light in Asian populations.

That matters for a Malaysian parent, because the 1999 paper itself notes that short-sightedness now reaches 70 to 90% in some Asian populations, so the question is not a theoretical one here. The reasons for the rise are set out in why childhood short-sightedness is rising.

What does the evidence say does affect short-sightedness?

Time outdoors is a well-supported habit, and it works on the chance of becoming short-sighted rather than on a child who already is. The American Academy of Ophthalmology reports that each additional hour spent outdoors per week was associated with a 2% reduction in the odds of childhood myopia. A Cochrane review of 2024 pooled five randomised trials with 10,733 children, mostly aged 6 to 9. At two years, 22.5% of children in the outdoor groups had become short-sighted, against 26.7% in the comparison groups. Its authors concluded that long-term interventions to increase time outdoors may potentially reduce the development of myopia, and that the evidence on slowing a child who is already short-sighted is of low certainty.

Two honest limits. The effect is modest, not dramatic. And neither source sets a daily target, so I do not give you one. The fuller version, including how to fit it into a school week, is in two hours outside, the cheapest myopia habit.

Family history is the other piece the lighting studies keep pointing to. Both 2000 reports found that short-sightedness in the parents is associated with it in the children. That is not a reason to panic. It is a reason for those families to get outdoors and to have a child's eyes checked rather than wait for a complaint.

So should I switch the light off?

For your child's eyes, you do not need to. If a night light makes a child feel safe, or lets you see to settle a baby, the short-sightedness evidence gives no reason to remove it. I would keep your attention on the things that do have evidence.

If you want one practical step, make it the outdoor time. If a parent is short-sighted, say so at your child's next eye check; how we test eyes before a child can read explains what happens. And if you want the other bedtime-and-eyes worries cleared away in one place, carrots, dim light and other eye myths parents still hear covers reading in poor light, sitting close to the television and a few more.

When your child is already short-sighted and you want to know what slows it, the answers are in the guide to myopia control in Malaysia. Nothing in it involves the bedroom lamp.

Common questions

References

1. Quinn GE, Shin CH, Maguire MG, Stone RA · Myopia and ambient lighting at night, Nature 1999 · www.nature.com
2. Zadnik K et al, CLEERE Study Group · Myopia and ambient night-time lighting, Nature 2000 · www.nature.com
3. Gwiazda J, Ong E, Held R, Thorn F · Myopia and ambient night-time lighting, Nature 2000 · www.nature.com
4. Saw SM et al · Myopia and night lighting in children in Singapore, Br J Ophthalmol 2001 · bjo.bmj.com
5. University of Pennsylvania press release on the 1999 study (ScienceDaily) · www.sciencedaily.com
6. Cochrane Database of Systematic Reviews · Interventions to increase time spent outdoors for preventing incidence and progression of myopia in children, 2024 · pmc.ncbi.nlm.nih.gov
7. American Academy of Ophthalmology Task Force on Myopia · Reducing the global burden of myopia by delaying its onset, clinical statement 2021 · www.aao.org

By Dr Chan Li Yen. General information only. It does not replace a consultation. If you are worried about your child's eyes or vision, please see an eye doctor.