FOR KIDS: Making light of sleep1

The light signals sent to your body’s master clock tell you when to be sleepy and when to be alert. But not just any light will do. The circadian clock can distinguish between different colors, or wavelengths, of light. Blue light — such as the light from the blue sky — is best for stimulating the circadian system. In experiments, people exposed to blue light become less sleepy and more alert.

Sunlight is an excellent source of blue light. Although the light from the sun looks white, it is actually a combination of many colors, including blue light. This might explain why stepping outside on a bright sunny day helps clear the fog from your head.

Exposure to the morning sun is best for synchronizing the body’s clock with the Earth’s natural 24-hour cycle of light and dark. If you wake early and get outside, the body’s master clock tends to shift earlier, says Mariana Figueiro, a scientist at Rensselaer Polytechnic Institute in Troy, N.Y. That means you’re alert when it is light outside and sleepy when it’s dark.

The problem is, adolescents and teens may have limited exposure to the morning light. Often, they are on a bus or in class during the peak morning hours. Recently, Figueiro ran an experiment to see how exposure to morning light affects the circadian clocks of middle school students. She traveled to Smith Middle School in Chapel Hill, N.C. This school’s building is designed to provide daylight throughout the entire building.

Half of the students in the group wore orange-tinted goggles during morning school hours for one week. The glasses allowed enough light for the students to see, but blocked blue light coming in through skylights. Students in the other group had full access to daylight.

Each day, the scientists measured how much light exposure each student received, using a special light meter placed on the headphones of the goggles. The researchers also gave students a series of tests to measure their reaction times and memory skills. And at the end of each day, the scientists collected some spit from each student.

The saliva was used to measure amounts of a hormone called melatonin. Hormones are the body’s messenger molecules. Melatonin is known as the “sleep hormone.” When it gets dim outside, your brain secretes melatonin, preparing the body for sleep. As kids mature, melatonin is secreted later and later in the evening. This makes it easier for teens to stay awake longer and later.