The Canadian WorkSafeBC released a human factors bulletin with information on
fatigue and how to prevent it in the workplace. Most people need 7.5-8.5 hours
of sleep every day, and when they don't get enough, their performance may
suffer. They may have slower reaction times and difficulty concentrating and
making decisions.

Studies have shown that people working the night shift get about 5 to 7 hours
less sleep per week than those working the day shift. The shortened periods of
sleep coupled with the natural tendency to be awake in the day means the sleep
in the day is not the same quality as night sleep.

More information

AplusA-online.de - Source: Canadian Centre for Occupational Health and Safety