Children’s eyes let in more light than adults’ eyes do.

It turns out that children’s eyes are anatomically slightly different. They let in more light, and a study in the journal Physiological Reports suggested that exposure to bright light before bedtime can throw their body clocks out of whack.

Lameese D. Akacem, an instructor at the University of Colorado, Boulder, who was the lead study author, said, “We know from a lot of studies done in adults, adolescents, schoolchildren, that the body clock is very sensitive to light exposure.” “Particularly in the evening, it tends to suppress the sleep-promoting hormone melatonin.” But it had not been studied in preschool age children.

It turns out that the lens that allows light into the eye “is a lot clearer in preschool children,” Akacem said. “The pupils are larger, which allows more light to hit the retina and a stronger signal to the clock.”

The lens accumulates protein as we get older. By the time we’re in our 40s, our eyes are dimming the light for us a little.

“One important takeaway is that parents should avoid having children exposed to very bright light before bedtime,” Akacem said.