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Today, most of our daily lives take place indoors and under artificial light. Daylight is no longer the natural pacemaker that it has been for our ancestors for thousands of years. However, our bodies are still designed to respond to light – and not just for the purpose of seeing.
Light also has a biological effect. It influences hormones, sleep, concentration, mood, and thus our health. This is precisely where the concept of Human Centric Lighting (HCL) comes in. It’s goal is to design artificial light in such a way that it not only illuminates rooms, but also supports people in their rhythms. That definitively sounds like progress. But on closer inspection, it becomes clear that there is often a gap between aspiration and reality—and not everything that sounds good is harmless.
Human Centric Lighting – HCL for short – literally promises to put people front an center in its goals. The term has been in use since the 2010s, when research findings on the biological effects of light began to attract more attention. Since then, it has appeared in specialist articles, standardization committees, and increasingly in the lighting industry’s marketing.
The idea behind it sounds convincing: light should not only provide sufficient brightness so that we can see, but also keep our internal clock in sync. This is because our bodies are sensitive to light—it determines when we are awake and productive and when we become tired. Daylight fulfills this role naturally, but it is often lacking in modern working environments.
This is where HCL wants to step in:
During the day, bright, rather cool light with higher blue components should promote activation and support concentration.
In the evening, warmer light colors and lower intensities should signal to the body that it is time to wind down.
Throughout the day, changing lighting moods are supposed to mimic the dynamics of daylight as closely as possible.
On paper, this creates a coherent concept: greater well-being, better performance and healthier rhythms, even for people who spend most of the day indoors. HCL is therefore considered a promising approach in many planning guidelines for offices, schools and healthcare facilities.
As convincing as the idea of human-centric lighting sounds, its implementation in practice often looks different. While the theory envisages replicating the entire course of the day and thus supporting people in their natural rhythm, in reality HCL is often greatly simplified: more blue for more alertness.
In offices, schools, and hospitals in particular, the main focus is on combating fatigue and increasing performance. The effect of blue light is often reduced to a single mechanism: blue light suppresses melatonin, which means people stay more awake and alert. But this view is too narrow—blue light affects much more than just melatonin release. It has a systemic effect on the entire hormone balance and can thus trigger reactions that go far beyond the internal clock.
Light expert Dr. Alexander Wunsch vividly describes how problematic this reduction is in his book “Die Kraft des Lichts” (The Power of Light):
(translated from the German original text) “Since then, terms such as “human-centric lighting” have been used to market lighting systems that are designed to create a “biologically effective” lighting situation for people by changing the blue components in the light depending on the time of day. The lighting industry has chosen melatonin as an indicator of the “biological effectiveness” of its cold artificial light.
The simple logic is: melatonin makes you tired, so we suppress melatonin release with blue-enriched light and suddenly workers are awake, productive, and in a good mood. However, the situation is not that simple, because during the day it is usually much too bright for melatonin to be released anyway. Furthermore, as Hollwich’s research shows, among other things, the effect of blue-enriched light does not stop at the internal clock and the pineal gland, but has much wider implications.
The stimulation of various core areas in the hypothalamus caused by blue light triggers a systemic stress response, which manifests itself, for example, in an increase in stress hormones in the blood. In principle, hypothalamic stimulation by blue-enriched light affects almost all hormones secreted by the pituitary gland, which is the central control center of the hormonal system.
In natural sunlight, the systemic stress response triggered by blue light ensures survival because it prepares the body for ultraviolet light and strong solar radiation:
Since blue and ultraviolet are linked via Planck’s curve, our bodies can indirectly infer the presence of invisible UV radiation from the brightness and measurement of blue light, because in nature, more blue also means more UV. However, when we are indoors in rooms lit with blue-enriched light, a false alarm is triggered via the hypothalamic tract – with far-reaching consequences.”
(Dr. med Alexander Wunsch, Die Kraft des Lichts, S. 135/136)
Targeted protection for screen use – blue light protection glasses can significantly reduce disruptive blue light emissions.
Comfortable lighting for everyday use – an LED with a continuous spectrum gives you more red light and less stress from blue.
Background information on regeneration—find out why near-infrared light is important for recovery in our detailed article.
The German Commission for Occupational Safety and Standardization (“Kommission Arbeitsschutz und Normung”, KAN) has been studying the biological effects of light for many years. Its statements clearly show that light can offer opportunities, but that it must be used with caution.
Back in 2015, KAN warned that there was insufficient evidence to establish requirements for artificial biologically effective lighting. Standardization was neither sensible nor permissible at that time. Priority should continue to be given to daylight, and artificial systems should only be used with caution. (Position paper 2015, updated 2022)
In 2018, KAN confirmed the biological effects of light, but emphasized that there were still major gaps in research. It remained unclear what the optimal dose, duration, and timing were—and what proportion of total daily light exposure was attributable to workplace lighting. (Literature review 2018)
Human Centric Lighting directly influences processes that determine our biological balance. This is because light not only controls our vision, but also our hormone balance—for example, the release of melatonin, which is important for sleep and regeneration, or cortisol, which makes us alert and active.
When used correctly, such stimuli can be helpful: a clear signal to wake up in the morning, support for concentration during the day. But when the focus is solely on productivity, other needs are overlooked. Our bodies need not only stimulation, but also rest, protection, and relaxation.
An example: In some offices, lamps with a high blue light component are used specifically to keep attention levels high. This works in the short term—but anyone who sits in the same light after eight hours of work takes the “wakefulness impulse” home with them and finds it harder to fall asleep in the evening.
The problem: While the short-term effect is measurable and desirable, potential side effects are more difficult to identify. Those who work in activating light on a permanent basis risk sleep disorders, chronic fatigue, and a system that is out of sync. And those are just the systemic effects. The high-energy blue light in this lighting can also endanger eye health. This makes HCL a tool that may increase performance but puts health at risk.
That’s why health must take precedence over productivity. Lighting should not become a tool that drives people in one direction, but should provide support in the best sense of the word – in harmony with the natural rhythm.
Human Centric Lighting showcases how important light is for our well-being. It emphasizes that lighting can be much more than just brightness: it influences our rhythm, our performance, and our health.
However, there is a significant gap between aspiration and reality. In practice, productivity is often the primary focus, while potential side effects are given insufficient consideration. Expert committees such as KAN and recent scientific analyses therefore emphasize that the effects are real, but research has not yet progressed to the point where it is safe to “tinker” with the biological rhythms of humans.
As long as we spend most of our daily lives indoors, the question of how we design artificial lighting remains crucial. Human Centric Lighting shows the potential, but the path to truly human-centered lighting is not yet complete. It is crucial that health takes precedence over productivity—and that we use light in such a way that it does not blindly drive us, but keeps us in step.
Image credits:
Title: -Ranilson Arruda via Canva.com
Blog: -Reception Desk by TrueCreatives via Canva.com
-Safety Gear by Dali Images via Canva.com
-Hand Reaching for the Sun by Aflo Images via Canva.com
-Zen Stones by iLexx von Getty Images Signature via Canva.com
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