BRIGHT LIGHT AFFECTS ALERTNESS AND PERFORMANCE RHYTHMS DURING A 24-H CONSTANT ROUTINE

The aim of the present study was to assess the stimulating effects of bright light (BL) on subjective and objective alertness. Eight subject s were exposed to either bright light or dim light (DL) during a 24-h constant routine (0900-0900). Bright light failed to modify either the 24-b course or the level of body temperature. Compared to DL, BL dela yed the circadian trough of motor activity by 2 h. During the night, r elative to the dim-light condition, BL significantly increased subject ive and objective (EEG test) alertness and improved performances. Thus , BL exposure partly counteracted the effects of sleep deprivation and /or the circadian trough on alertness and performances. During the day , BL only improved the mood and motivation levels. However, the time c ourse of mood and motivation was not affected by the BL exposure, a no cturnal circadian trough occurring at 0630 in both light conditions.