Photic Effects on Sustained Performance

The advent of space exploration requires attention to the adaptability of human circadian rhythms in the unique environment of space. Circadian disruption, related to altered sleep work cycles and accelerated solar clues, can lead to fatigue that may impede mission success particularly as the duration of space flights increase. Research is described which evaluates manipulating environmental light intensity as a means to attenuate nocturnal fatigue. A counter-balanced, within subjects design was used to compare 9 male subjects exposed to dim (100 lux) and bright (3000 lux) light conditions. Oral temperature values were greater for the bright light group over the dim light condition. Melatonin levels were suppressed by bright light treatment. Also, the frequency of eye blink rate was less for subjects during bright over dim light exposure. Light exposure was without effect on subjective fatigue. However, irrespective of light condition, significant effects on confusion, fatigue and vigor mood dimensions were found as a result of 30 hr sleep deprivation. The findings suggest that bright lights, may be used to help sustain nocturnal activity otherwise susceptible to fatigue. Such findings may have implications for the lighting arrangements on space flights during the subjective night for astronauts.