To determine the measurement duration
and frequency required to reliably quantify the typical personal light exposure
patterns of children and young adults.
Ambient light exposure
data were obtained from 31 young adults and 30 children using a wrist-worn light sensor configured to measure ambient light exposure
every 30 seconds for 14 days. To examine the influence of measurement duration
upon light exposure
, the daily time exposed to outdoor light levels (>1000 lux) was initially calculated based upon data from all 14 days and then recalculated from 12, 10, 8, 6, 4, and 2 randomly selected days. To examine the influence of measurement frequency
, the outdoor exposure time was calculated for a 30-second sampling rate and again after resampling at 1-, 2-, 3-, 4-, 5-, and 10-minute sampling rates.
Children spent significantly greater time outdoors (44 minutes higher [95% CI: 26, 62]) compared to adults (P
= .001). Children spent more time outdoors during the weekdays (13 minutes higher [−7, 32]) and adults spent more time outdoors during the weekends (24 minutes higher [7, 40]) (P
= .005). Calculating light exposure
using a lower number of days and coarser sampling frequencies did not significantly alter the group mean light exposure
> .05). However, a significant increase in measurement variability occurred for outdoor light exposure
derived from less than 8 days and 3 minutes or coarser measurement frequencies in adults, and from less than 8 days and 4 minutes or coarser frequencies in children (all P
< .05). Reducing measurement duration
seemed to have a greater impact upon measurement variability than reducing the measurement frequency
These findings suggest that a measurement duration
of at least 1 week and a measurement frequency
of 2 minutes or finer provides the most reliable estimates of personal outdoor light exposure
measures in children and young adults.