Subjective alertness and sleep quality in connection with permanent 12-hour day and night shifts.

Day workers reported significantly greater sleepiness during workdays compared to night workers.

• Day workers went to bed later and rose earlier than night workers.
• Both groups had similar total weekly sleep duration, but their sleep patterns differed.
• Day workers averaged 5 hours of sleep before the first shift and 6 hours after subsequent shifts.
• Night workers had longer sleep durations, averaging 9 hours before their first shift and 6.5 hours after others.
• Day workers experienced difficulties awakening before shifts, while night workers showed little variation in sleep quality.

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