Human Centric Lighting (HCL)

The term "Human Centric Lighting" refers to lighting applications which focus on human well-being in a particular way. Awareness of the influence of lighting on health and well-being of people has increasingly developed due to the impact of new, far-reaching findings from intense research activity. These findings lead to a new definition for good light. In addition to creating good visual conditions and spatial light effects, the spectral composition of light during the course of the day must be considered in planning many applications.

Human beings have evolved under daylight over several million years of development history. In their evolution, humans have adapted to daylight and its highly varied effects just as they have adapted to a natural day/night rhythm.

Over the past 100 years, humans have now – contrary to the natural day/night cycle – created a global 24-hour society, in which we are seemingly independent of the diurnal rhythm, true to the slogan "light turns the night into day". This independence, must be evaluated very critically. For reasons of health and well-being, lighting should always be geared to natural light and purposefully integrated into the course of the day. The most vital aspect about this are the biological effects of light on our inner clock. But also the emotional or psychological effects of lighting must not be neglected.

As late as the year 2000, an additional receptor was discovered in the eye, which plays an important role in this biological, non-visual impact of light. The "new" receptor, a photosensitive ganglion cell not involved in the actual visual process, reacts particularly to light wavelengths in the short-wave "blue" region of the spectrum of ca. 480 nm (see section "Optical radiation"). Since its discovery, science and industry have been intent upon understanding the non-visual impact on human beings and the current state of knowledge is gradually being reflected in light applications. Particularly the discovery of the protein melanopsin, which serves to make the newly discovered ganglion cells photosensitive as a photopigment, has influenced the concept of "melanopic efficiency" of light.

This much is clear: Composition and intensity of the spectrum emitted by various light sources have different effects on human beings. Consequently, the right lighting can boost well-being and positively influence moods. Activation and relaxation can also be promoted through lighting.

Figure 1.38: The ganglion cells especially sensitive to the blue light component are located in the lower region of the retina. They are not involved in the visual process, however, they serve as signal transmitters for our "inner clock".

The melanopic effect of light can mainly improve health-related aspects such as activation, recreation and overall well-being (non-visual effects) while the visual effect can evoke and support emotions. The combination of non-visual and visual support of human beings defines the term "Human Centric Lighting".

In practice, four basic applications can be distinguished.

  • Melanopically effective light to maintain health
    The human day/night rhythm can be supported by light. Just like daylight, purposeful lighting can maintain and promote health and performance capability through changes in light colour and intensity.

  • Melanopically effective light for activation
    Lighting supports attention and concentration capability. Through the activating effects of colder light colours in particular, cognitive performance capabilities can also be enhanced.

  • Melanopically effective light for recreation
    Light has an activating effect, but also actively contributes to recreation and relaxation. Well-being can be enhanced by adjusting the lighting to individual needs, for example by changing to warmer light colours.

  • Light that inspires emotions
    Lighting showcases, accentuates and creates spaces. Creating varied light atmospheres can inspire emotions of elation or cosiness, which enhance well-being.

The term "melanopically effective light" does not only describe a light situation characterised by absolute data on physical and photometric key values. It rather refers to the temporal and relative variation of the latter, which  supports the phsyiology of the human circadian rhythm (see section

Human Centric Lighting therefore is distinct from purely technical lighting wherever light should have a psychological, physiological or psychobiological effect on human beings.