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Light at night impacts a person’s ability to fall asleep because it prevents the body’s production of melatonin, a hormone our bodies produce at night to help us feel tired and fall asleep. Exposure to light at night disrupts that melatonin production, which makes it more difficult to fall asleep, even after the lights go out.
This study is the first to show that even dim lighting also affects children’s melatonin levels before bedtime. The low level of light measured in this study begs the question: Are night lights, long used to dispel fears of the dark, just as bad?
The study focused on 36 children between 3 and 5 years of age who kept a consistent sleep schedule for eight nights as researchers measured natural melatonin levels. On the ninth night, children received one hour of light exposure in the hour before their regular bedtime. Researchers chose the hour before the children’s normal bedtimes to mimic the time when exposure to an electronic device or other light might occur in the children’s everyday lives.
The lighting amount ranged from 5 to 40 lux. This measurement range is similar to an electronic “tablet at half brightness, held one foot away from the eye, [which] is about 25 to 30 lux (at full brightness, it can be up to 100 lux),” says research Dr. Lauren Hartstein of UC Boulder’s Sleep and Development Lab.
Study results show that the children produced significantly less melatonin after the low level of light exposure: The children’s melatonin levels were 69% to 98% lower after light exposure in the hour before bedtime when compared to melatonin levels on nights without light exposure.
Researchers also found the children’s melatonin levels were on average 50% lower for almost an hour after the light was turned off when compared to their melatonin levels on nights without night lights.
The study notes that young children’s sensitivity to light may be related to the developmental stage of the eye. Children’s pupils are larger and clearer than those of adults, which lets light into their eyes more easily. Their higher sensitivity to light can keep the children’s melatonin levels lower, making it harder for the children to feel sleepy.
Young children may be afraid of the dark and ask for night lights to soothe them. While no light is best in the moments before bedtime, parents have options. Since 2011, the Federal Trade Commission has required that lighting packaging state the bulbs’ watts and lumens to foster energy-conscious purchases. Parents can use these labels to choose bulbs based on lumens rather than watts, as the U.S. Department of Energy recommends. Lumens may be more helpful in these decisions, as lumens are a measurement indicating a bulb’s brightness, while watts are a measurement of its electricity usage.
Researchers recommend reducing light intensity in the hour before bedtime. This may help the children produce more appropriate melatonin levels and support their readiness for sleep.
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