Quantifying the biological impacts of nightlights: implications for sleep and circadian health in children.

Given the widespread use of nightlights, we characterized an assortment of popular products to evaluate their potential to disrupt sleep and circadian rhythms in children. Spectral irradiance was measured for 25 top-rated nightlights (79 settings) under laboratory (source-level) and simulated bedroom (typical use) conditions. Nightlights varied in form (handheld, projector, tabletop, wall plug-in) as well as intensity and color settings. Melanopic equivalent daylight illuminance (EDI) estimated circadian input and was compared against biologically relevant thresholds for pediatric sleep. Across conditions, melanopic EDI values spanned several orders of magnitude, from 0 lx to >100,000 lx, with some devices varying substantially by setting. With source-level characterizations, only 3/25 products consistently remained below 5 lx melanopic EDI (levels known to phase shift circadian rhythms and suppress melatonin in children), and 2 also met the <1 lx consensus nighttime recommendation for adults. Under typical-use conditions, 14/25 products remained below 5 lx melanopic EDI (11 were <1 lx) on at least one setting, with most being red-toned, low-intensity, and positioned farther from the bed, though many of those would not support vision. Clear clinical guidance, public health recommendations, and improved product labeling standards are needed to reduce circadian disruption and promote healthier sleep in children.