While researchers know the lack of time spent outdoors is a risk factor for myopia, less is known about specific indoor and outdoor light levels, and the impact of sun-protective measures. To fill this gap, researchers in Singapore recently confirmed that light levels outdoors were higher than indoors—and remained well above the threshold illuminance for myopia prevention even with adequate sun-protective strategies.

The team used a child-sized mannequin head to measure light levels with and without sun-protective equipment across a wide range of indoor and outdoor environments, including in a park, under a tree, on a street, under fluorescent illumination with a window and under white LED-based lighting without a window. They then compared the light levels children experience during their daily routines.

They found that outdoor light levels ranged between 11,080 lux and 18,176 lux, while indoor levels were only 112 lux to156 lux. Light levels above 1,000 lux are protectant against myopia, they noted, which is easily achievable in the shade under a tree (5,556 lux to 7,876 lux) and with a hat (4,112 lux to 8,156 lux). They found that sunglasses yielded lower lux levels between 1,792 and 6,800 lux—still above the threshold for myopia control. Although these readings were weaker than those obtained with tree shade and a hat, the team adds that they were still 11 to 43 times higher than indoors.

“Recommendations on spending time outdoors for myopia prevention with adequate sun protection should be provided while partaking in outdoor activities, including protection under shaded areas, wearing a hat or sunglasses, sunscreen and adequate hydration,” the study authors concluded.