Abstract
PURPOSE: Considering that time spent outdoors is protective for myopia, we investigated how ambient light levels reaching the eye varies across 9 outdoor and 4 indoor locations in 5 different environmental conditions. METHODS: Illuminance (lux) was recorded using a lux meter under conditions of weather (sunny/cloudy), time of a day (7:00,10:00,13:00, and 16:00 hours), seasons (summer/winter), and sun protection (hat and cap) in outdoor and indoor locations. Nine outdoor locations were "open playground", "under a translucent artificial-shade", "under a porch facing east", "under a porch facing south", "under a big tree", "between three buildings", "within 4 buildings", and "canopy". As a ninth outdoor location, "Under a glass bowl" in the outdoor location was used as a simulation for "glass classroom model" and measurement was taken at the floor level only to determine in overall the illuminance conditions with glass covered on all sides. The 4 indoor locations included "room with multiple large windows", "room with combination light source", "room with multiple artificial lights", and "room with single artificial light". RESULTS: The overall median illuminance level (median; Q1-Q3) recorded in 9 outdoor locations was 8 times higher than that of all indoor locations (1175;197-5400 lux vs. 179;50-333 lux). Highest illuminance in outdoor locations was recorded in "open playground" (9300;4100-16825 lux), followed by "under a translucent artificial shade (8180;4200-13300 lux) and the lowest in "within 4 buildings" (11;6-20 lux). Illuminance under 'Canopy', 'between three buildings' and 'within four buildings' was similar to that of indoor locations (<1000 lux). Time of the day, weather, season, sensor position and using sun protection did not alter illuminance to change from high to low level (>1000 to <1000 lux). Among indoor locations, illuminance in "room with multiple large windows" crossed 1000 lux at a specific time points on both sunny and cloudy days. CONCLUSIONS: Illuminance levels in outdoors and indoors varied with location type, but not with other conditions. Given the variation in illuminance in different locations, and the impact it may have on myopia control, appropriate detailed recommendations seems necessary while suggesting time outdoors as an anti-myopia strategy to ensure desired outcomes.