Pre-bedtime lighting as a predictor of sleep outcomes in preschool-aged children

Abstract

Studies that examine the effects of light on subsequent sleep tend to be done in controlled laboratory settings, rather than in the lighting conditions humans sustain in day-to-day life; rarer still are environmental light/sleep studies in children. The purpose of this study was to examine the effects of evening environmental lighting on subsequent time to sleep onset latency (SOL), sleep efficiency (SE), and total sleep time (TST) in preschool-aged children. Children who screened positive for behavioral sleep problems (n=411) wore an actigraphy watch, which collected light and sleep data, for one week. Environmental light before bedtime was associated with SOL (p <0.01), but not SE or TST. Light sustained up to, but not beyond, 35 minutes before bedtime predicted SOL. For the 15-minute period pre-bedtime, children whose upper quartile readings were 1 to 10 lux added 6 minutes (p<0.001; 95% CI 3 to 9) to SOL compared to children whose upper quartile readings were <1 lux. This trend continued with increasing lux exposure: at an upper quartile of ≥75 lux, children added 15 minutes to SOL (p<0.001; 95% CI 7 to 24). Our suggestion that even slight differences in the relatively narrow range of at-home lighting (<1 to 200 lux) in the 35 minutes before habitual bedtime can make a significant impact on sleep onset latency in preschool-aged children, but that it may not be necessary for parents to restrict lighting >35 minutes before habitual bedtime, adds new knowledge to the body of sleep research.