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The circadian rhythm develops from the second year of life onwards.

In reality, it is not so easy to design a circadian supporting artificial lighting system,
as it depends on many other factors. The findings regarding the effect on humans are
not yet sufficient in this context and require additional research. Besides visual pho-
toreceptors, a third receptor was discovered at the beginning of the 21st century: spe-
cial ganglion cells in the retina. These aforementioned ipRGCs contain a certain pro-
tein, the so-called melanopsin, which reacts sensitively to certain blue components in
light. If blue light in the right composition and direction and with sufficient intensity
strikes enough non-visual ganglion cells, the production of the sleep hormone mela-
tonin, which plays an important role in fatigue and sleep, is reduced. The result is an
activation of the organism and a preparation for the day. The natural circadian rhythm
can be disrupted by a lack of daylight throughout the day and too much artificial light
with high blue components in the evening - emitted by smartphones, notebooks,
tablets, and televisions, for example. The consequences are often sleep problems, fati-
gue during the day as well as concentration problems and a higher susceptibility to
infections. In principle, existing knowledge of the biological/melanopic effects of light
can and should be used to design lighting systems in order to positively support
people in their natural circadian rhythm. From a purely technical point of view, the
course of daylight in some areas can already be simulated almost artificially. However,
studies on how this affects humans are still under development. The overriding goal
of HCL-based lighting is to dynamically adjust artificial lighting throughout the day to
positively support people in their circadian rhythm. This can be implemented in dif-
ferent ways, but all concepts have one thing in common: Activation in the evening
should be avoided so that the body is prepared for the night's rest. What if the daily
rhythm differs from the natural circadian rhythm? Here too, HCL-based lighting
systems are likely to be able to support this trend.

One of the most important care facilities in Northern Germany

For the first time, the aforementioned Human Centric Lighting criteria are being
applied throughout the new ward building of the children's hospital "Auf der Bult" in
Hanover. The complex structure of different areas with partly conflicting requirements
was developed together with architects, colour designers, and light planners. The
interaction of light and colour is important for an optimal spatial effect. The quality
of the light also has a decisive influence on the quality of the colour and thus also on
the quality of the room. The "Auf der Bult" lighting system, which focuses on people
and their natural needs in terms of lighting technology, is based on the colour concept
of colour designer Markus Schlegel. However, during the implementation it became
clear from the concrete practical example that many questions still remain unanswe-
red with regard to the biological effect of light. This concerns both technical, planning
and individual issues of the users. A lighting system planned under the given premises
should therefore still be coupled with a review - an evaluation - in order to further
investigate the effect on humans. In 1863, socially committed citizens of Hanover foun-
ded the charitable foundation "Hannoversche Kinderheilanstalt" (HKA), which today
runs the children's and youth hospital "Auf der Bult". With more than 40,000 young
patients treated each year, the children's hospital is one of the most important medi-
cal care facilities in northern Germany. Together with architects, colour designers, and
lighting planners, a common room concept was created. Studio DL's lighting concept
is based on extensive research into circadian rhythm and other non-visual effects of
light on humans. In all patient rooms, room lighting is provided by luminaires with a
"tunable white" function. The lighting scenarios created follow the daily hospital rou-
tine: during the day, there is an activating, cold white lighting atmosphere that
changes into a calming lighting atmosphere with warm white light from 4 p.m.
onwards. Indirect lighting close to the floor disturbs the patient's sleep as little as pos-
sible, which has a positive effect on the healing process on the one hand and mini-
mises the strain on the staff caused by awakened children on the other. However, in
hazardous situations, the light level and colour temperature can be raised to a maxi-
mum at any time, so that staff can always react and work appropriately. The day
rooms can also be used as patient rooms if required, which is why the room lighting
here is also controlled by "tunable white" scenarios. The planning team used circular
luminous ceilings at intersections, which display diffuse, slightly blurred, changing
animations, intended to distract from fears and worries and vary throughout the day.