Circadian Rhythm and the Role of Lighting

In September 2016, the fluorescent lamps on the International Space Station will be replaced with LEDs that can change light intensity and color spectrum based on whether the astronauts need to be lured to sleep or roused awake. Since the astronauts see the sun rise and set every 45 minutes but get virtually no exposure to sunlight, the study seeks to implement an artificial lighting schedule to regulate the astronauts’ sleep-wake cycles. Will it work?

The answer depends on how the characteristics of light that we can currently control influence the body’s circadian rhythm: the physical, mental, and behavior changes that happen on a roughly 24-hour cycle. One of these changes is the sleep-wake cycle. Circadian rhythms are complex interactions of internal factors—such as hormonal releases and changes in body temperature—and external cues, such as changes in light and sound.