What is the brightness of daylight needed for myopia control?

More than two hours of outdoor time, particularly with adequate brightness of daylight, might curb myopia progression. Some non-outdoor settings with sufficient brightness could help too.

(Article Updated Feb 14, 2024)

In the last post, we talked about how outdoor activities under daylight could help children reduce the risk of myopia progression. Since then, I have done some more research to better understand the activities that could be considered. 

Several well-controlled studies showed significant effects of outdoor light exposure on myopia progression when children have two (2) hours of intermittent outdoor light exposure per day and 8-15 hours per week, including recess time, physical education time, and additional outdoor time after school.^{1, 2, 3, 4} 

But what is the brightness of daylight required? What activities could be considered? 

How to measure the brightness of daylight?

To understand how bright it should be (illuminance), we will need to understand how it is measured. Brightness is measured by the amount of light (lumens) falling on a unit area. The light of one candle radiating through one steradian is one lumen. And, one lumen per square meter is one lux.

Studies indicated that the slowing of myopia progression was seen when exposure was at least 1,000 to 3,000 lux with a brighter light level associated with a shorter exposure time needed.^1,4 

Note: Make sure to have sufficient sun protection and harmful UV rays. 

Brightness of daylight in different outdoor settings

I searched to figure out the different settings that could be at least 1,000 to 3,000 lux. Here is what I found summarized below. 

The summary corresponds to the outdoor activities recommended by healthcare professionals, including sports, gardening, a walk around the neighborhood, trail hiking, or even a picnic. 

Brightness of daylight in different indoor settings

Interested in what possible non-outdoor activities could count toward my son’s activity tracker, I downloaded a lux meter app and tested it during my family trip to Boston.  (Learn more about the MyoAssist app -- an outdoor activity tracker)

The reading from the app seemed to match the reported lux level for most of the settings. There were some settings in which I had interesting findings. 

*Tinted sunroof glass

On our way to Boston, it was a sunny day. So we pulled back the car’s sunroof shade. Even with the tinted sunroof glass, we had 3,000 lux. However, on our way back, it was overcast. The lux level dropped to 500. This indicated that on a sunny day, riding in a car could be included in the tracker – assuming not using smart devices or reading. 

Furthermore, while we were in Boston having lunch at the Yankee Lobster restaurant, we were in an area with a translucent roof. The lux level reached >5,000. To my son’s delight, having some tasty fish and chips provided him with “high-quality” daylight and lots of yummy omega-3.

Overall, it was a great trip to Boston. My son had fun in Boston and exceeded his daily outdoor activity target – even without including the time in the car. Furthermore, we not only learned more about Boston Tea Party and visited many historical sites but also found that having lunch at the right restaurant with the right dish could help control his myopia.

Want to stay connected on the newest happening? Join me @

Facebook group: www.facebook.com/groups/myopia/ 

Pinterest board: https://www.pinterest.com/clearsightcorner/

1. Wu, Pei-Chang et al. “Myopia Prevention and Outdoor Light Intensity in a School-Based Cluster Randomized Trial.” Ophthalmology vol. 125,8 (2018): 1239-1250. doi:10.1016/j.ophtha.2017.12.011
2. Ho, Ciao-Lin et al. “Dose-Response Relationship of Outdoor Exposure and Myopia Indicators: A Systematic Review and Meta-Analysis of Various Research Methods.” International journal of environmental research and public health vol. 16,14 2595. 21 Jul. 2019, doi:10.3390/ijerph16142595
3. Ulaganathan, Sekar et al. “Influence of seasons upon personal light exposure and longitudinal axial length changes in young adults.” Acta ophthalmologica vol. 97,2 (2019): e256-e265. doi:10.1111/aos.1390
4. Read, Scott A et al. “Light Exposure and Eye Growth in Childhood.” Investigative ophthalmology & visual science vol. 56,11 (2015): 6779-87. doi:10.1167/iovs.14-15978