The chronotype is a measure of where the internal clock of a person lies relatively to the external time (clock time) [RPZW19].

In common tongue, chronotypes are known as owls (late chronotypes) and larks (early chronotypes). Since sleep is one of the most obvious outputs of the internal clock, sleep phases are most commonly used to determine the chronotype. Alternatively, the time dependent level of alertness can be considered.

 

Chronotypes are nearly normally distributed with slight surplus of late chronotypes [FLMR00].

Figure 1 shows a distribution of chronotypes using the sleep phases without external restrictions (alarm clock). The colors encode the respective chronotypes. For representation it is used either sleep time (time of falling asleep to time of waking up, scale on the top) or midpoint of sleep (mid-point between falling asleep and waking up, scale on the bottom). The representation via midpoint of sleep has the advantage that it is independent of the individuals sleep duration. When using sleep a sleep duration of 8 hours is uniformly assumed. However, how many hours of sleep a person needs per night is independent of his chronotype. The chronotype only defines when someone sleeps, not how long. Late chronotypes do not sleep longer than early ones, they only sleep later.

 

The chronotype is a measure of where the internal clock of a person lies relatively to the external time (clock time) [RPZW19].

In common tongue, chronotypes are known as owls (late chronotypes) and larks (early chronotypes). Since sleep is one of the most obvious outputs of the internal clock, sleep phases are most commonly used to determine the chronotype. Alternatively, the time dependent level of alertness can be considered.

 

Chronotypes are nearly normally distributed with slight surplus of late chronotypes [FLMR00].

Figure 1 shows a distribution of chronotypes using the sleep phases without external restrictions (alarm clock). The colors encode the respective chronotypes. For representation it is used either sleep time (time of falling asleep to time of waking up, scale on the top) or midpoint of sleep (mid-point between falling asleep and waking up, scale on the bottom). The representation via midpoint of sleep has the advantage that it is independent of the individuals sleep duration. When using sleep a sleep duration of 8 hours is uniformly assumed. However, how many hours of sleep a person needs per night is independent of his chronotype. The chronotype only defines when someone sleeps, not how long. Late chronotypes do not sleep longer than early ones, they only sleep later.