The effect of pre-sleep lighting on melatonin, sleep and alertness of the crews in the enclosed cabins in the evening with the cumulative effect of light

The lighting field has seen tremendous growth in basic and applied research on the non-visual effects of light in the last more than 20 years, but lighting design for occupants in isolated, confined and enclosed environments a long time has still not been further developed. We investigated the effects of three-hour pre-sleep lighting intervention on melatonin, alertness and sleep of 24 healthy participants (23.58 ± 0.7 years; 12 males) for three days, within an enclosed cabin structure. A between-subjects design was used throughout the experiment, which included four lighting conditions (m-EDI: EL1, 200 lux; EL2, 20 lux; EL3, 40 lux; EL4, 10 lux), where CCT of EL1 and EL2, EL3 and EL4 were approximately the same. The results showed that whereas lighting conditions had almost little impact on indicators of morning, they had a significant impact on melatonin, objective alertness and sleep at night. The EL2 lighting had significantly higher melatonin suppression at night, and EL3 had significantly longer total sleep time and shorter R-period ratio, compared with EL4. The EL1 with high m-EDI had a considerably greater sleep efficiency and sustained higher objective alertness at night, but significantly lower subjective alertness compared with the other three lighting. Also, EL1 had significantly higher melatonin suppression compared with EL3 at night, and there was circadian rhythm phase delay. Two potential thresholds were implied to exist in night lighting intervention, one between 20–40 lux m-EDI affecting the cumulative effect of melatonin suppression, and one between 40–200 lux m-EDI enforcing circadian rhythm phase delay.