Newswise — Settling youngsters down to sleep at night isn't always easy. Recent research suggests that the amount of exposure children have to bright light in the hour leading up to bedtime — whether emanating from light bulbs or electronic devices — can have a big impact on sleep-related behavior.
There's chemistry behind it. Our circadian rhythm — a kind of 24-hour internal brain clock that cycles regularly between sleepiness and alertness — employs melatonin, the body's natural sleep-inducing hormone. Melatonin is highly sensitive to light. As daylight dims toward the end of the day, our bodies are programmed to react to the reduction of light by increasing the production of melatonin. It's nature's way of ushering us toward sleep. Artificial light, however, can disrupt the circadian cycle by inhibiting the production of melatonin.
Research into the effects of light on preschool-age children found that youngsters are particularly sensitive to light exposure in the hour prior to bedtime.1 (Children's clear crystalline eye lens and large pupil size render them generally more sensitive to light than adults.) According to some researchers, evening light exposure, with its melatonin-suppressing effect, may increase the likelihood of sleep disturbances in preschool-age children.2 When little ones shuffle out of a dark or dimly lit bedroom to tell parents "I'm thirsty" or "I heard a strange noise," the bright light they encounter has been found to reduce their melatonin production, making it all that much harder for them to fall asleep when back in bed. Even reading bedtime stories in a brightly lit room can make it harder to fall asleep at story's end. Dimming the ambient light, in both the child's room and whatever spaces they might walk into, may be a wise approach whenever possible.
Mobile electronic devices, with their bright white screens, pose a similar risk. As many as 90% of preschool-age youngsters use devices, often during the hour before bedtime.3 But it's not only preschoolers; youngsters of all ages find themselves glued to screens as the very last activity of their day. Studies found that following light exposure, melatonin remains suppressed for nearly an hour after the lights go off — time for tossing and turning and missing out on essential shut-eye. Parents might declare the last hour prior to bedtime a device-free period, or insist that youngsters slide the brightness setting way down on their handheld electronics.
1 Akacem, L.D., et al. "Sensitivity of the circadian system to evening bright light in preschool-age children." Physiological Reports, Vol. 6, No. 5. March 2018. https://physoc.onlinelibrary.wiley.com/doi/10.14814/phy2.13617.
2 Akacem, L.D. et al. "Bedtime and evening light exposure influence circadian timing in preschool-age children: A field study." Neurobiology of Sleep and Circadian Rhythms, Vol. 1, Issue 2, Nov. 2016. https://doi.org/10.1016/j.nbscr.2016.11.002
3 Vandewater, E. A., et al. "Digital childhood: electronic media and technology use among infants, toddlers, and preschoolers." Pediatrics 119, 2007.