Psychophysiological effects of a brief nocturnal light exposure

This study compared the effects of a brief pulse (60-minute) of three full spectrum light intensities (1000, 500 and 30 lux) and two green light intensities (1000 and 500 lux) administered between 0200 and 0300 hrs. Ten participants were involved in this repeated measures study. Each participant experienced one condition every week for five weekends. Sessions began at 1800 hours and ended at 0600 hours the following day. Outside of the 60-minute exposure period, each session was spent in 30 lux white light. Oral temperature, salivary melatonin, cognitive performance and subjective mood were sampled throughout the sessions. Analysis revealed that all of the experimental light conditions significantly reduced salivary melatonin concentrations immediately following the pulse. This effect was not maintained beyond the duration of the light pulse. There was no significant effect on oral temperature. There were also no significant effects on cognitive performance and subjective mood, though some positive trends were observed. These results argue that brief, moderate intensity, pulses of either green or full spectrum light are sufficient to suppress the normal nocturnal rise in melatonin. However, the level of suppression obtained does not translate into significant improvement in cognitive performance or subjective mood.