Home Medizin Neue Forschungsergebnisse entlarven den Einfluss von Farbe auf die innere Uhr des Menschen

Neue Forschungsergebnisse entlarven den Einfluss von Farbe auf die innere Uhr des Menschen

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Vision is a complex process. The visual perception of the environment is generated through a combination of various light wavelengths, which are decoded in the brain as colors and brightness. Photoreceptors in the retina first convert light into electrical impulses: in sufficient light, cones enable sharp, detailed, and colored vision. Rods only contribute to vision in poor lighting conditions, allowing for differentiation of various shades of gray, but with significantly less accuracy. The electrical nerve impulses are then relayed to ganglion cells in the retina and then to the visual cortex in the brain via the optic nerve. This region of the brain processes the neural activity into a colored image.

What Influences the Internal Clock?

However, ambient light not only enables vision, it also influences our sleep-wake cycle. This process is predominantly influenced by specialized ganglion cells, which, like cones and rods, are light-sensitive and particularly reactive to short-wavelength light at approximately 490 nanometers. If light consists exclusively of short wavelengths between 440 and 490 nanometers, we perceive it as blue. When short-wavelength light activates the ganglion cells, they signal to the internal clock that it is daytime. The intensity of light per wavelength is crucial; the perceived color is not relevant.

„However, the light-sensitive ganglion cells also receive information from cones. This raises the question of whether the cones and thus the light color also influence the internal clock, as the most noticeable changes in brightness and light color occur at sunrise and sunset, marking the beginning and end of a day,“ says Dr. Christine Blume. She conducts research on the effect of light on humans at the Center for Chronobiology at the University of Basel and is the lead author of a study examining the effects of different light colors on the internal clock and sleep. The research team from the University of Basel and TUM has now published their findings in the journal „Naturmenschliches Verhalten.“

Bright Colors Compared

A study on mice in 2019 suggested that yellow light has a stronger influence on the internal clock than blue light.

Dr. Christine Blume, University of Basel

In humans, the primary effect of light on the internal clock and sleep is likely mediated through light-sensitive ganglion cells. „However, there is reason to believe that the color of light, encoded by the cones, could also be relevant to the internal clock,“ says Christine Blume.

To investigate this, the researchers exposed 16 healthy volunteers to blue or yellow light and as a control condition, white light, for one hour late in the evening. The light stimuli were designed to activate the color-sensitive cones in the retina differently and in a very controlled manner. However, the stimulation of light-sensitive ganglion cells was the same in all three conditions. Differences in light effects were therefore directly attributable to the respective stimulation of the cones and ultimately, the color of light.

„This method of light stimulation allows us to cleanly separate the light properties that might play a role in the effect of light on humans,“ says Manuel Spitschan, a professor of chronobiology and health at the Technical University of Munich, who was also involved in the study.

To understand the effects of different light stimuli on the body, the researchers in the sleep lab determined whether the participants‘ internal clocks had changed depending on the light color. They also assessed how long it took for the participants to fall asleep and how deeply they slept at the beginning of the night. The researchers also inquired about their fatigue and tested their reactivity, which decreases with increasing sleepiness.

Ganglion Cells are Critical

The conclusion: „We found no evidence that the variation in light color along a blue-yellow dimension plays a relevant role in the internal clock or sleep of humans,“ says Christine Blume. This contradicts the results of the aforementioned mouse study. „Rather, our results support the findings of many other studies that light-sensitive ganglion cells are most important for the internal clock in humans,“ says the scientist.

Manuel Spitschan sees the study as an important step towards translating basic research into practice: „Our results show that it is most important to consider the effect of light on light-sensitive ganglion cells in the planning and design of lighting. Cones, and therefore, color, play a very minor role.“

It remains to be seen whether the color of light has no influence on sleep, even if the parameters change, such as extending the duration of light exposure or at a different time. Questions like these should be answered by subsequent studies.


Journal Reference:

Blume, C., et al. (2023). Effects of calibrated blue-yellow light changes on the human circadian clock. Natur menschliches Verhalten. doi.org/10.1038/s41562-023-01791-7.

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