licht.wissen 19 No. "Impact of Light on Human Beings"

But even if we skip lunch, we hit a performance
“low” at midday. In the early after<strong>licht</strong>.<strong>wissen</strong>
<strong>19</strong>
<strong>Impact</strong> <strong>of</strong> <strong>Light</strong> on Human Beings
07 08
Biological rhythms
Controlled by the brain, the same programme is re-run day after day in the human body. An internal clock controls
not only our sleep and waking phases but also our heart rate, blood pressure and mood. Every cell and every organ
has a rhythm <strong>of</strong> its own that needs to be synchronised regularly with the outside world. Brightness during the day
and darkness at night provide the most important cues.
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Many bodily functions are cyclical – both
in human beings and in other living creatures.
Chronobiologists distinguish between
three major categories based on length <strong>of</strong>
cycle:
Ultradian rhythms span only a few hours.
Examples include times <strong>of</strong> day and
hunger, sleep and waking phases in infants.
Circadian rhythms are geared to day and
night. They last around 24 hours (circa =
approximate, dies = day).
Infradian rhythms have cycles longer than
24 hours, e.g. the changing seasons.
Circadian rhythm
Human beings and their bodily functions
have daily and seasonal rhythms. From
individual cells to entire organs, every unit
controls its own time programme. Breathing
and heartbeat, waking and sleep – all
biochemically controlled functions have
their individual highs and lows over the
course <strong>of</strong> the day.
Shortly before we wake up, our body
temperature, blood pressure and pulse
rate rise. Around an hour later, the body
produces stimulating hormones. Doctors
know that the risk <strong>of</strong> heart attack is at its
greatest between 10 a.m. and noon.
But this is also the time <strong>of</strong> day when we
find brain teasers like Sudoku easiest and
when short-term memory is at its best.
So it is a good time for an exam or job
interview.
Stomach acid production peaks between
noon and 2 p.m., facilitating digestion <strong>of</strong> a
midday meal. When producing acid, the
stomach consumes so much energy that
the rest <strong>of</strong> body feels fatigued.