The human biorhythm and daylight

With the first rays of sunshine in the morning, the day begins regularly for billions of people. Man has become accustomed in his evolution to the daylight and its very different effects as well as to the natural day-night rhythm. Many processes in the organism were adapted to this tact. In the annual time change, each of us can empathize with our own body, how much this rhythm defines our well-being. Our organism is depending on this circadian (daily rhythmic, well-rehearsed) rhythm and acts accordingly.

Hormone levels, blood pressure, mood and motivation change according to the internal clock and thus influence our health and well-being. In the past 100 years, humans have created a global 24-hour society, contrary to the natural day-and-night rhythm. In our modern civilization, the light no longer ends in the evening and the electric light defines our lives to a very high degree today. This apparent independence of time of day is, as we know today, extremely critical. A problem that is being dealt with in “Human Centric Lighting” or “biologically effective light”.

So light seems to be the clock of our biological clock. But how does it assert its influence on humans?

Since the millennium we know that light affects us even more than we thought until then. Lighting should therefore always be oriented to the natural daylight and be integrated into the course of the day. The essential aspect is the biological effect of light on our biological clock and the associated emotional and psychological effects on our body.

The discovery of ganglion cells

Only in 2000 did scientists find a new receptor in the upper layers of the retina in the eye. They were called “ganglion cells”. The interesting thing about these ganglion cells is that they found a new photoreceptor that was not involved in the actual visual process. Nevertheless, it responds particularly to light wavelengths in the short-wave, “blue” region of the spectrum of about 480 nm.

This is evoked by a photoprotein that acts in these ganglion cells. It’s called melanopsin and it’s what controls our hormones. A sensational discovery among the researchers. Because now it was clear that when light enters the eye that melanopsin ensures that our “inner master clock” (suprachiasmatic nucleus) receives a nerve impulse. This nucleus, in turn, clocks the pituitary gland from where nerve pathways also run to switch points in the spinal cord, the pineal gland and the hypothalamus. The light impulse is thus an important clock, which rhythmizes many unconscious processes.

Since its discovery, science and industry are concerned with the understanding of the non-visual effect on humans and now want to technically recreate the effects of natural lighting. The positive effects should be used – so light color and light intensity should adapt to the circadian rhythm throughout the day.

One thing is clear: the composition and intensity of the light and color spectrum emitted by different light sources have different effects on humans. Thus, proper lighting can increase well-being and positively influence mood. Activation or relaxation can also be supported by light. The combination of non-visual and visual support through light to humans defines the new term “Human Centric Lighting.” Light is thus designed and controlled to optimally support and activate these processes in the body.

Practical application of Human Centric Lighting

Since in the morning and noon, the high-intensity light and increased levels of blue support the performance, the light in indoor areas should be adjusted accordingly. For example with a dimmer, light color control and light direction. In the evening, however, the strength should decrease and the proportion of red should rise. This supports the human being in the preparation for the sleep phase.

The light direction plays a role insofar as the melanopsin-containing receptors are sensitive especially in the lower part of the retina. Thus a wide-area lighting from above is recommended during daytime. In the evening, individual spots with a warmer light color are more appropriate for optimally relaxing the body and preparing it for the night.

The effort of research has paid off. Applications of biologically effective light are already showing great results. At workplaces and schools, some pilot projects have already been successfully launched. Research and industry continue to work on ever better energy-saving and cost-effective solutions for private purposes.

A biologically effective light, is always a smart system, which supports the circadian rhythm depending on the time of day and according to personal needs and habits the light controls and reproduces accordingly. Human Centric Lighting is thus differentiated from purely technical lighting wherever light is supposed to have a psychological, physiological or psychobiological effect on humans. Man has known electric light for nearly 150 years. Now the era of “biologically effective light” has begun.