Well designed artificial lighting can reduce negative effects on the body’s circadian clock, and might even bring health benefits. Compared with conventional incandescent or fluorescent bulbs, LEDs use less energy, last longer and contain no glass or mercury, negating the risk of glass shards or toxic metal floating through the space station should the bulbs break in zero gravity. But researchers also hope that the new lighting system will help astronauts to sleep better at night and to stay alert during the day. The problem that engineers are trying to address is that there’s no ‘day’ or ‘night’ in space. The ISS circles Earth every 90 minutes or so, which provides astronauts with frequent opportunities to see the Sun rise and set, but also wreaks havoc on the body’s roughly 24-hour, or circadian, clock. Among space flight’s many deleterious effects on health, disturbance of the circadian rhythm and the sleep deprivation that accompanies it have emerged as considerable worries. ...