Indoor and outdoor lighting and visual development

• Outdoor light is much brighter than indoor lighting, with the brightness appearing to support normal childhood visual development.
• Spending at least two hours per day outdoors is protective against myopia development and progression in children and teenagers.
• Sun protection is still important when spending time outdoors – wearing a hat, sunglasses and staying in the shade.
• Blue-light blocking coatings for spectacle lenses (glasses) can improve visual comfort in some people, but claims that they protect eye health are not supported by evidence.

Much evidence points towards the benefits of increasing time spent outdoors in preventing or delaying myopia in children and teenagers.¹

Myopia is an eye condition which causes blurred far vision, and is also known as short-sightedness or near-sightedness. Once myopia develops in children and teenagers, it typically deteriorates every few to several months. In most cases, this worsening continues until the late teens or even early 20s.² This is called progressive myopia, which is a significant concern to quality of life in children and teenagers, and also poses risks to long-term eye health.³

Spending at least 13 hours per week (just under 2 hours per day) outdoors has been shown to reduce the likelihood of children developing myopia, across multiple research studies.¹

Increasing time spent outdoors has also been shown to have a positive effect on slowing the deterioration of vision in children with myopia.⁴ This can provide an additional benefit for children and teenagers undergoing myopia control treatment, to reduce their myopia progression.

Time spent outdoors also has physical and psychological benefits for children. A study in Sweden found that children who spent more time outdoors in nature and green spaces had better mental health and a lower risk of developing mental health disorders in their teens and into adulthood.⁵

The main reason why outdoor time appears to support healthy visual development in children and teens is the brightness of the light. This benefit appears to be there regardless of the physical activity (or not) undertaken while outdoors, and also independent of how much reading or near work a child is doing.¹

Outdoor light is different from indoor light as it is substantially brighter - it can be 500 times brighter than indoors. Even when under shade, wearing a hat and sunglasses when outdoors, light levels are still at least 11 times higher than indoors with fluorescent or LED lighting.⁶

Sun protection is extremely important for children. Around one-quarter of lifetime ultra-violet (UV) exposure occurs before age 18⁷ and children wear sunglasses less than a third as frequently as adults.⁸ Excessive sun exposure can lead to eye diseases in later life such as eye surface disorders, cataract and age-related macular degeneration. This means it's important to set up good sun protection habits from a young age.⁹

The good news is that a child or teenager can get the benefit of the brightness of outdoor light even when being sun safe. Research has shown that if a child is sitting in the shade while wearing a hat and sunglasses, the level of brightness reaching the eye is still far brighter than in any indoor situation, and enough to help protect against myopia.⁶

Sitting by a window may make for a nicer view, but it doesn't appear to provide the brightness of light needed to be beneficial to childhood visual development compared to being outdoors. One study showed that even next to a large window, outdoor light was far brighter than that achieved indoors.⁶ It is useful to try try to maximize natural light indoors, but this does not replace time spent outdoors.

Studies have shown that an average of two hours per day outdoors protects children and teenagers' eyes from developing myopia.¹⁰ This level of outdoor time can support healthy children’s vision by reducing the risk of developing myopia. Any outdoor time is beneficial, and it all adds up, so breaks at school and even an outdoor mode of travelling to and from school can help. 

We don’t yet know what the benefit is of spreading this time out over the week, or by getting more outdoor time on the weekend to balance things out. The research so far has reported on both - daily time and weekly time - so for now it’s safe to assume that if the week gets too busy, increasing time outdoors on the weekend is going to be helpful.^1,10

Blue-light blocking coatings on spectacle lenses (glasses) can reduce eye strain for some people, when spending a lot of time looking at back-lit screens. There is a small amount of evidence that they can improve sleep quality in people with self-reported insomnia, but may not have an effect in those with normal sleep patterns.

Claims about these coatings protecting the health of the retina have not been supported by evidence.^11,12 The best advice is to pick this type of coating if your child or teenager feels more comfortable looking through it at a screen.

Sources of glare when a child or teenager is reading or using a screen can slow down reading speed.¹³ Glare can come from direct and indirect light, such as windows, desk lamps and ceiling lights. It is recommended that spaces used for homework and study have no sources of glare within the field of vision. This means placing desk lamps outside the field of view so the light can't be seen in peripheral vision when reading or studying.

Position desks at right angles to a window, or off to the side, rather than facing into a window. A window behind a desk may be suitable if reflections from a computer screen can be minimized. Overhead ceiling lights should also be behind the desk user or off to the side and not visible in peripheral vision when working at the desk.¹⁴

The amount of lighting needed can depend on the difficulty of the task and size of the print or screen being used. Childrens' and teenagers' eyes transmit more light through to the retina (the light-sensitive layer at the back of the eye) than adults,¹⁵ so may need less lighting to see comfortably than their parents for the same visual task.

Our circadian rhythm is the 24-hour cycle which ensures we are awake and asleep at the ideal times of day. The biggest trigger for feeling alert in the morning, or sleepy at night-time, is the level of light received by the eyes. Children aged 9 to 15 years who were termed to be in pre-puberty or mid-puberty were much more sensitive to light exposure at night-time than older teenagers. In these younger kids, evening light exposure suppressed the production of melatonin, the important neurochemical which prepares our body to go to sleep. This group of children are therefore more sensitive to sleep disruption from even low levels of indoor lighting before bed time.¹⁶

In China, where the prevalence of childhood myopia is at 80%-90%, there are schools experimenting with glass-walled ‘Bright Classrooms’ to simulate outdoor lighting conditions inside where the students spend most of their days. We are still learning about whether different types of indoor lighting could influence eye growth in children (it’s been shown to be the case in animal research models) so for now, maximizing natural lighting and increasing outdoor time is the best action to take.

New smartwatch technology¹⁷ is being developed to help encourage children and teenagers to spend more time outdoors, by monitoring the brightness of the light exposure to a smartwatch worn by the child. This may be a part of managing healthy visual development for children and teens in the future - ensuring the most at-risk kids are setting and achieving goals to spend enough time outdoors.

Here are three things to help in providing your child or teenager with their best chance for healthy eyes and good vision.

1. Two hours outdoors. Spend at least two hours per day, on average, outdoors. If this sounds like a lot, remember that break times and sport at school will add up, and aim for more outdoor time on the weekend. Even a small increase by less than an hour a day can have a dose-response benefit for children’s vision.¹⁰
2. Be sun safe. Ensure sun protection outdoors, as this won’t impact the beneficial effect of time spent outdoors and protects the eyes and skin from harmful UV rays. This includes a hat, sunglasses, sunscreen and seeking the shade.
3. Manage glare and screen time. This includes setting up homework and study spaces to be free of direct light sources in the field of view, and avoiding screen time for one to two hours before bedtime to support good sleep.

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