Ambient light level varies with different locations and environmental conditions: Potential to impact myopia.
Level 5 - mechanism / opinion, no new human data
Physical environmental measurement study without human subjects or clinical outcomes (by design analogy, Level 5).
PubMed 34234353 · doi:10.1371/journal.pone.0254027
What was done
Researchers measured ambient illuminance (lux) with a lux meter across 9 outdoor locations (open playground, under translucent artificial-shade, under east-facing porch, under south-facing porch, under a big tree, between three buildings, within four buildings, canopy, and under a glass bowl outdoor simulation of a glass classroom) and 4 indoor locations (room with multiple large windows, combination light source, multiple artificial lights, or single artificial light). Measurements were assessed across weather conditions (sunny vs. cloudy), time of day (7:00, 10:00, 13:00, 16:00), season (summer vs. winter), and sun protection (hat and cap).
What was found
Overall median illuminance (median; Q1–Q3) across the 9 outdoor locations was 8-fold higher than across indoor locations (1175 lux [197–5400] vs. 179 lux [50–333]). Outdoor illuminance was highest in the open playground (9300 lux [4100–16825]) and under translucent artificial shade (8180 lux [4200–13300]), and lowest within four buildings (11 lux [6–20]). Illuminance under a canopy, between three buildings, and within four buildings fell below 1000 lux, resembling indoor levels. Time of day, weather, season, sensor position, and sun protection did not shift illuminance categories across the 1000 lux threshold. Among indoor settings, only a room with multiple large windows exceeded 1000 lux at specific time points.
Why it matters
Because outdoor time is commonly recommended to slow myopia onset, these data show that not all outdoor settings deliver high light levels. Broad recommendations to spend time outdoors may fail to achieve the intended light dose if activities occur in deeply shaded or built-up urban microenvironments.
Limits
No human participants or refractive error outcomes were evaluated. Measurements for the glass-classroom simulation were restricted to floor level only. The study used discrete static sampling conditions rather than continuous dynamic personal light dosimetry.
Cited by
- supports Outdoor light lux intensity on a cloudy day substantially exceeds the lux intensity of indoor building lighting.