Two studies were designed to investigate the carryover effects of daylight on performance and self-reports of sleepiness. The effects of daylight and of darkness were compared independent of the effects of simultaneous periodic, 1-hour exposures to narrow-band blue and red lights over the course of 26-hour sessions. Nighttime performance on a 54-minute tracking task, but not subjective sleepiness, was significantly better following exposure to daylight. There was no differential effect on performance or sleepiness from exposure to the blue or red lights. Eight of the participants returned to experience a completely dark session and a replication of the daylight and intermittent blue light session. Nighttime performance and subjective sleepiness were significantly worse for the dark session than for daylight-plus-blue sessions in both studies.