brightness, spectral composition) and lacks variation related to geographical dissemination, seasonal change and the 24-hour light-dark cycle. Artificial light is quantitatively and qualitatively different from natural light (e.g. Our results suggest that during long-term daylight deprivation, retinal sensitivity to blue light increases, whereas circadian rhythm stability decreases and sleep-wake timing is delayed.Ĭompared with the long-term evolution of humans under natural light-dark cycles, the use of artificial lighting has – on an extremely short time scale - tremendously augmented and often replaced natural light. Sleep and wake times (as assessed from rest-activity recordings) were significantly delayed after the first month without sunlight (p < 0.05). Circadian rhythm analysis revealed a significant decay of intra-daily stability, indicating more fragmented rest-activity rhythms during the dark period. Overall, our data showed increased pupil responses under scotopic (mainly rod-dependent), photopic (mainly L-/M-cone dependent) as well as bright-blue light (mainly melanopsin-dependent) conditions during the time without direct sunlight. Rest-activity cycles were continuously monitored by activity watches. The pupil responses to different light stimuli were used to assess retinal sensitivity changes. We aimed at testing whether retinal sensitivity, sleep and circadian rest-activity will change during long-term daylight deprivation on two Antarctic bases (Concordia and Halley VI) in a total of 25 healthy crew members (mean age: 34 ± 11y 7f). Long-term daylight deprivation such as during the Antarctic winter has been shown to lead to delayed sleep timing and sleep fragmentation.