Sixteen Sunrises a Day: NASA’s Lighting Fight to Reset the Astronaut Clock

The ISS orbits Earth every ~92 minutes, giving astronauts 16 sunrises and 16 dusks per Earth day, which disrupts their natural circadian clocks and leads to sleep loss and reduced cognitive performance. NASA combats this with LED lighting that shifts color and intensity to cue wakefulness or promote sleep, and by covering windows during rest to minimize real-time light cues. A 2016 study of 21 long-duration astronauts found they averaged about 6 hours sleep per night (vs. ~7 on Earth), with many using sleep meds and experiencing circadian misalignment that correlated with decreased performance during critical tasks. Despite engineering advances, spaceflight remains hard on the human body, and lighting alone has not fully solved the sleep-and-clock challenge for astronauts.