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This experiment was designed to establish whether lighting provided by a daylight-simulating skylight could be used to enhance the task performance and mood of night-shift workers. Subjects performed a series of cognitive tasks, gave subjective ratings of their mood and had their core temperature measured six times during each shift, for three successive nights, under the same lighting condition. Each shift ran from 00.00 hours to 07.59 hours. The subjects also kept a daily diary recording their general health, times of sleep and sleep quality for the complete period of the experiment. Four lighting conditions were experienced: a fixed low-illuminance condition; a fixed high-illuminance condition; an increasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from dawn to midday; and a decreasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from midday to dusk. There was a three day rest period before exposure to each lighting condition. The high, increasing and decreasing illuminance conditions produced higher core body temperatures and greater subjective arousal than did the low illuminance condition, on all three nights. The high- and decreasing-illuminance conditions improved the performance of complex cognitive tasks relative to the low and increasing illuminance conditions, on all three nights. There was no difference between the lighting conditions for the performance of simple cognitive tasks. The high illuminance condition led to a greater delay in going to bed following the shift than did the low-illuminance condition.
Boyce et al. (Mon,) studied this question.