It's hard to get a good night's sleep in orbit. Astronauts on the International Space Station see a sunrise every 90 minutes or so, which leads to some seriously messed-up internal clocks. Sleeping pills help a bit, but now scientists think they can game circadian rhythms more naturally—and effectively—with new light bulbs.

Sleep is regulated in part by melatonin, a hormone the body produces when the eye detects darkness. “Light is the most important cue for resetting the clock,” neuroscientist Steven Lockley says. In a replica of the ISS crew quarters, photobiologists installed color- and brightness-adjustable LEDs, and volunteers came in for light baths at different intensities. The results: The lower the light, the more melatonin in volunteers' blood, potentially improving their sleep.

Now researchers are testing how different wavelength combos affect alertness. Red-shifted light allows sleep, and bluish light wakes you up, so the next question is whether astronauts can sleep better and then perform better with wavelength-controlled illumination. By 2016, NASA plans to install the bulbs in the real crew quarters—and its astronauts can get some well-deserved shut-eye.