Abstract:
Purpose To examine the light exposure patterns of school aged children in relation to refractive error. Methods School-aged children (13-14 years old, n = 12) were issued with self-contained light meters that recorded the ambient light levels every 10 seconds (HOBO Pendant UA-002-064, Onset Computer Corporation, USA). The ambient light levels were collected every 10 seconds over seven days (one period). Measurements were made in three periods over three consecutive months in winter. Cycloplegic autorefraction and axial length measurements were made at the beginning and end of the three month study. Results Ambient light level recordings indicated that while children spent only a small amount of time outside (10.65 ± 2.52 hours per week, or 5.88 ± 1.39% of the total time; mean ± 95% CI, n = 12) these outdoor periods accounted for a large proportion of their total light exposure (4.72 × 107 ± 1.65 × 107 lux, or 87.95 ± 3.72% of their total light exposure). The subjects were exposed to only 5.72 ± 1.86% of the total available light on average over the measurement period. There was a significant correlation between the amount of time spent indoors (between 10 and 1000 lux) and the cumulative light exposure obtained indoors (R2 = 0.945). There was, however, a poor correlation between the amount of time spent outdoors (>1000 lux) and the cumulative light exposure obtained outdoors (R2 = 0.296). Refractive error was not significantly correlated with cumulative light exposure (R2 < 0.001). There were no significant correlations between the rate of change in light levels and refractive error. Discussion and Conclusions A small amount of time spent outdoors is associated with a large proportion of daily light exposure. While predictable levels of light exposure are obtained indoors, there is a great degree of variability in the amount of light received by going outdoors. Thus, a small amount of extra time spent outdoors can disproportionally affect the total light exposure received per day. Further investigations of the quality (e.g. spectral composition) and quantity (e.g. yearly exposure, differing seasons, etc.) of light received by school-aged children are warranted.